I don't want it just to be about 40k, as awesome as it is. I'm thinking the British troops from the revolutionary war will be the cannon fodder, and each platoon will be led by a handful of marines. The PCs will also do battle against a mutated Ben Franklin, who has been seduced by chaos with promises of the presidency he never managed to achieve. Maybe he's a devotee of Slaanesh and has eight voluptuous breasts with toothed maws instead of nipples. I also want them to team up with Jesus Christ at some point. Or possibly fight him. Even God's only son is not immune to the taint of chaos!