I know a little about Orks and their weird group psychic thing where painting their ships red to go fast really makes them faster, and their tech only works because they think it should. But then I guess Orks aren’t even in this game.
I get that it’s a violent, black-vs-grey universe. I think it’s the originator of the term grimdark? The emperor is some immortal Mr House asshole who’s worshipped as a god, which powers some of their tech and protects them from chaos via his psyker shit? And he’s kind of a fascist, but it’s that or bloody chaos?
Rogue traders seem like somewhere between a privateer and a baron, plundering tithes in their castle-ships and acting as an arm of the Imperium in backwater space?
There are more wizards than I expected. Not sure if these mechanicus dudes are pulling “Temples of Syrinx” thing, or they know how the tech works but not why so they worship it? Or if it’s actually machine spirits?
Anything super foundational that I’m missing?
You’ve got the important foundational elements. The other big event is the Horus Heresy, where about half of the Emperor’s sons fell to Chaos and started a huge civil war that left the Emperor in his current half-dead state, but the imperial bureaucracy keeps on chugging.
The other thing to keep in mind is that the world of Warhammer 40k has been evolving over decades of novels, tabletop games, and video games made by multiple authors. As a result, the canon is vast and occasionally self-contradictory.
If you want to know more, I highly recommend the Ciaphas Cain books (novels with a comedy streak) and a silly fan series called If the Emperor Had a Text-to-Speech device.
"Record keeping is shit and we aren’t even sure what year it is any more so don’t take anything at face value " is the new canon, so the canon being a mess is canon now.
I second reading or listening to the Ciaphas Cain books, since they bring that pinch of satire with them.
You also get to explore most races from the 40k universe quite quickly.
Quite quickly?
I would say with almost unseemly haste
As always, Cain tends to downplay the situation in his usual manner.