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?