There is some pricey dlc for this one eh...
Well it *is* a Paradox game, so yes.
That being said, I'll point out two things:
1.) Nearly every single DLC released so far has a "Positive" or "Very Positive" rating on Steam. This is highly unusual for Paradox titles -- even when the main game itself is highly-rated (CK3, CS1, EU4, Stellaris, etc.), their DLC's are typically much more hit-and-miss. The fact that the DLC for Age of Wonders 4 breaks this trend strongly implies they're probably worth the money one might spend on them. (Not that I won't still wait for a sale, of course.

)
2.) More pertinently, none of the DLC is necessary. Seriously, there's already so much content in the main game that it's ridiculous. Between the different races & realms, and the fact that you can (and should!) create your own, once you feel up to it -- the customization options for each are pretty nuts -- means that AoW4 has (quite frankly) a huge amount of replayability.
Honestly, if this is just what the base game is like, I think my brain might explode when I start getting the DLC as well. Thankfully, I'm in no hurry to do so, as there's already more than enough here to keep me happily occupied for a long time to come.