I’ve read a lot of Wookieepedia articles. I haven’t directly experienced a whole lot of Star Wars novels or comics, because there are enough of them that I’d never be able to make a complete survey of the field anyway, and as with most massive expanded universes, the general consensus is that most of it isn’t very good.
But I do feel like you can break Star Wars down into a few important eras (real world eras, that is, in-universe eras are also a thing but are not what this post is about), and that consuming the highlights of each era will give you a pretty good look at what Star Wars has been. These should be required reading/viewing/playing for creators helming major projects in the franchise. Even though most audiences have only consumed a fraction of these, a creator who balks at consuming a few dozen hours’ worth of content is showing the kind of contempt for other creators working in the same franchise that indicates they’re a bad fit for the job. It’s not so much that the information transmitted is vital as the willingness to honor the legacy of those who came before. If all copies of the Thrawn Trilogy suddenly evaporated into powder, you could probably get by just fine without them, but if someone is unwilling to read three books before creating a new installment in the same shared universe, that speaks poorly to their willingness to play nice with other creators in such a way as to create a sustainable shared universe.
The first era is the 70s and 80s, when the Original Trilogy released and basically nothing else. There were video game adaptations and spin-off comics, but the Expanded Universe didn’t really exist yet and none of what nascent side media did exist turned out to be particularly notable in the long run.
The First Expansion era came in the 90s, brought about by the Thrawn Trilogy. This era largely explored the immediate aftermath of the Original Trilogy, which means a lot of it has been decanonized. At the same time, creators more respectful of what came before than JJ Abrams or Rian Johnson have been desperately recanonizing as much of it as possible, including the character of Grand Admiral Thrawn himself. Other significant media from the era is Star Wars: Dark Forces (and at least some of its sequels, although it’s hard to pin down exactly when that series petered out and stopped being relevant enough to be required playing), the X-Wing vs. TIE Fighter series, and possibly the Thrawn duology. The Thrawn duology did lots of important work in establishing what the first two decades of the New Republic were like, but now that all of that has been firmly decanonized, most of what you need to know about characters like Thrawn and Mara Jade can be gotten from the first trilogy.
Dark Forces’ canonicity sits in a weird place, with Rogue One having clearly decanonized the early levels where you retrieve the Death Star plans, but the Dark Trooper Project that drives the plot of the latter two-thirds of the game has been recanonized by the Mandalorian. Kyle Katarn and his specific adventures uncovering the Dark Trooper Project are in canon limbo. Even if the whole game gets totally decanonized (for example, the dark troopers get an alternate origin story which, like Rogue One and the Death Star plans, is totally incompatible with Dark Forces), it was really popular at the time and a creator working in the universe should take the time to become familiar with it (if they’re bad at video games, there’s probably a story compilation on YouTube that’ll get the important points across, and worst-case scenario there’s probably someone on the crew who can throw such a video together over a weekend).
You’ll probably want to throw Shadows of the Empire on there as well, although I’m skeptical of how much its impact was because audiences really liked it and how much was because it was a heavily marketed multimedia crossover event. I don’t know if anyone’s cared much about it since the Phantom Menace dropped in 1999, overshadowing the scale of its marketing spectacle. May as well read the novel or play the game or something if you have time, just to be thorough, but this one can be left out if you’re worried about time.
A lot of stuff from this era can be left as non-canon. There’s not really a cohort clamoring for the return of the Yuuzhan Vong, and the original second Galactic Civil War has all the same problems as the Disney Trilogy’s version but worse. You don’t need a Dark Nest Crisis. It’s good that the people in charge at the time had the presence of mind to terminate the Ssi-Ruuvi conflict after one book, and it would’ve been even better if they’d thought better of greenlighting that book in the first place.
From 1999 to 2005 we have the prequel era, when the prequel movies themselves are coming out. The vast majority of notable media from this era is a direct tie-in to the movies themselves and you can mostly just watch those movies and get what you need to. You could also probably skip Attack of the Clones, and you only need Phantom Menace because it’s needed to understand the impact of Qui-Gon Jinn and Darth Maul.
I really like spin-off video games like Bounty Hunter and Racer, others like Clone Wars (other than the titular conflict, no relation to the TV show), Starfighter, and Jedi Starfighter are okay, and apparently there are some spin-off comics that are good, but none of them present the kind of required reading/viewing that the Thrawn Trilogy or even the X-Wing novels do. There is one small exception: The 2003 Clone Wars animated series (the one by the Samurai Jack guy) is very well regarded and also very short. If you’re really absolutely desperate for time you could leave it out, because all of its major characters are also in the Prequel Trilogy and none of its story beats are likely to be critical even to a story taking place during the Clone Wars, but it’s both short and beloved, so leaving it out probably speaks poorly to a creator’s priorities. There’s also a lot of expansion novels and comics released in this era, but to the best of my knowledge (and it is worth noting that my knowledge of the comics in particular is limited), none of them are considered uncontroversially good. An extremely thorough creator would still want to read the highlights, but that’s true of basically everything short of the Christmas Special.
However, this era also overlaps with its successor. From 2003-2014 is the Second Expansion. This era is partly defined by continued expansion of the Clone Wars era, with the TV show originally running from 2008 to 2014 and games like Republic Commando releasing in 2005, but the reason this era starts in 2003 is because that’s when Knights of the Old Republic released. Knights of the Old Republic is certainly required playing for creators working in the era and even someone working in other eras should at least get someone to put together a highlight reel of important story moments. Likewise, while the entire Clone Wars series is not required viewing, watching a greatest hits series of its best regarded episodes certainly is.
KotOR II was of questionable canonicity even when it released (the pre-Disney Star Wars canon structure immediately enshrined it for no better reason than that it was an official video game in the brand, but the way it plays Hell with the timeline makes it seem like even its own creators wanted it to be an AU – though in fairness, it’s hard to make out what the creators were planning through the half-finished state of the game), but it’s considered one of the best and most nuanced depictions of the Jedi, Sith, and the Force in the franchise. A creator might reasonably want to reject its depiction of the Force, but they should do knowing and understanding what that depiction is.
The Old Republic can largely be skipped. Even in the most generous of interpretations, it, like, the Dark Forces series, becomes less and less prominent the more expansions deep it gets, and even taking only the core game by itself, it suffers the Thrawn Duology problem where yes, it’s pretty good, but you get the basic idea from its predecessor so it’s hard to justify calling it required playing. If you’re specifically doing something with the Galactic Cold War era you should probably play (or watch the highlights of) its core release and all expansions, but also that whole era is a mess warped and contorted around the needs of the MMO’s expansion release schedule, with the initial conflict swept aside so that future content would be nearly identical whether you had initially supported the Republic or the Sith.
The one-two punch of the prequel trilogy and Knights of the Old Republic led to a lot of spin-offs carving out their own new era. Expansion of the timeline had happened before, but almost always in service to plots clustered around the Original Trilogy and its aftermath. After fifteen years of novels and comics, that cluster on the timeline started to expand very far away from the Battle of Endor, but it was in 2006 that we got comics about Cade Skywalker that jumped the timeline ahead by 75 years, two out of our three depictions of the New Sith Wars came in 2006 and 2010, and Dawn of the Jedi (as the name implies, set long before even KotOR) started in late 2010. It’s worth noting that this era did not invent the idea of using other eras as a setting. KotOR itself took inspiration from Tales of the Jedi, a 90s-era Dark Horse comics series with exactly that premise, and the New Sith Wars’ first depiction came in 2001 when a comic was written to expand upon the lore of one of the later Dark Forces games, but KotOR’s success has resulted in many additional series of comics not directly tied to the background of another, more established era (I’ll admit that this might just be an optical illusion caused by putting all comics of this type from the First Expansion under the Tales of the Jedi label while Second Expansion comics with similar premises each got their own series, which might be making the latter appear more numerous than they are – I didn’t stop to count). None of them are especially prominent, however, and are required reading only for people working specifically with those eras (and such people are surely a fan of the comics already, otherwise why would they bother with such obscure spots on the timeline?).
This era also had the Force Unleashed. Much like Shadows of the Empire before it, I don’t think it’s required playing. It made a big splash at the time because there was a lot of marketing behind it and there were no mainline movies or similarly titanic releases around to compete, and people liked it when it came out, but it faded from memory quickly.
From 2015 to 2019 is the slightly short Sequel Trilogy era (although you might instead call the OT era bloated, since it gobbles up the void between RotJ and the first Thrawn book when the latest movie remained the most prominent thing happening right now not because it continuously dominated discussion, but by default). Like the Original Trilogy and Prequel Trilogy before it, the release of new movies immediately overshadows everything else going on. Unlike those two trilogies, it also includes two spin-off movies, Rogue One and Solo, and a spin-off TV show, Rebels.
It’s really hard to say how much of these are required viewing, because the Sequel Trilogy was the beginning of near-open hostility between creators. Disney casually obliterated almost everything the 90s era had created, while JJ Abrams and Rian Johnson squandered their one shot at a better New Republic era by using their movies to undercut each other’s interpretation of Star Wars rather than collaborating. Rey, Finn, and Po are perfectly good characters, and could be salvaged from their tire fire of a trilogy the same way Anakin was salvaged from Attack of the Clones partly by Revenge of the Sith, but mostly by Clone Wars, but if that happens it’ll probably be better to make the salvage job required viewing and ignore the ST.
I don’t know exactly what Star Wars creators are thinking or feeling, and of course no one’s voicing spite for the Mouse in public interviews, but the demolition of canon in 2014 seems to have engendered at least some degree of spite for the ST era – that, or the ST era is so aesthetically and thematically similar to the OT era that nobody sees any reason to use the controversial First Order era when they could use the stylistically identical Galactic Empire era. Whereas the PT inspired lots of spin-off works expanding on its era, the Sequel Trilogy’s release years are remarkably barren of anything to do with its own era besides novelizations of the films.
This carries forward into the Third Expansion of 2017-the present – although the Reclamation might be more apt. Starting in 2017, Timothy Zahn has started writing novels set in the Clone Wars and the Galactic Empire, not the First Order’s reign, which, parallel to similar efforts in Star Wars: Rebels, reintegrate Grand Admiral Thrawn into canon. 2019’s The Mandalorian is set in the immediate aftermath of the fall of the Empire, closer to Return of the Jedi than to the Force Awakens, and restores some lost bits of Dark Forces and firmly integrating the previously more self-contained 2008 Clone Wars into the timeline moving forward. Spin-off video games like Jedi: Fallen Order and Squadrons are set firmly in the time of the Empire and the New Republic (but prior to the formation of the First Order), even though the latter in particular could easily have been Resistance vs. First Order instead of Rebel Alliance vs. Galactic Empire. The upcoming Obi-Wan Kenobi is set during the reign of the Empire. Rogue One and Solo released during the Sequel Trilogy, but the total of absence of any reference to the sequel trilogy (despite i.e. Darth Maul, a prequel character, making an appearance) grounds them more firmly in the style of the Third Expansion/Reclamation than the Sequel Trilogy.
Star Wars’ Second Expansion carried a torch for the First, but I think it’s notable that the Third’s torch-carrying has been defined less by building upon what came before and more by a desperate scramble to preserve it from uncaring new creators. It’s kind of hilarious looking continuity complaints about the Clone Wars TV series being things like “Anakin says he’s never been carbon frozen before, but a tie-in comic has him carbon frozen as part of a plot to infiltrate a Separatist base, and that’s clearly set before Ahsako Tano was his apprentice and therefore before the entire run of the Clone Wars show!” Where the whole problem can be resolved by ignoring one line of dialogue. Or even “Gardulla the Hutt is apparently still alive during the Clone Wars, but in Bounty Hunter she’s killed by Jango Fett ten years before the war began!” Where you can just assume that Gardulla survived the encounter, or even that it’s a different Gardulla the Hutt (maybe it’s a common name). And then the ST comes along and suddenly it’s all “how do we salvage the entire character of Grand Admiral Thrawn?”