[Rhaalidor]

Sorry, but when I hear "Fire Warriors", I think of TAU. Wait 'til the Ordo Xenos gets a hold of that.

As for your fluff, it borders on greatness. The chapter could still be based on Ultramarine or Salamanders geneseed. And, you can wait to see how the story unfolds, like when they are hunted by Deathwatch, and have to turn Renegade to survive. They aren't really Choatic, but they aren't readily accepted by the Loyalist chapters after the Inquisition puts up the Wanted poster.

And, who is Keyser Soze, I mean Mulciber?