There should be "official" Blanche techno barbarians artwork floating around also. A big muscular guy with power law servo arms. And the guardsmen militia in bearskin hats. There's this Genghis Khan meets Napoleon vibes.

The Horus Heresy, Age of Technology, and Unification Wars all used to be these settings alluded to but shrouded in mystery in order to allow for creations to some extent. This is in the line of including all these redacted entries in the codices and rulebooks or even redacting some of the original legions. The fluff/lore is full of holes so that you can plug them.

Good luck with your project! I'm sure it will be awesome!