I'd be interested in joining as well! I'm a big fan of the Black Crusade tabletop variant, so I look forward to seeing how it works as a pseudo-freeform!

As to characters, if you're after beings of note that would have followings and the like, my first idea is to play as a living saint who led a crusade into the Eye of Terror millenia ago, and got lost in and overwhelmed by the warp, corrupting both her and her crusade to the forces of chaos.

If you're not a fan of that, an Inquisitor or Canoness would work just as well I guess.