From the announcement there will be 6 playable factions, each of the Chaos ones + Kislev and Canthay on the "good guys" side. There will also be a preorder faction that'll be released at the same time(can get the preorder bonus up to 1 week AFTER launch, so you can wait to see people's impressions instead of relying on press/influencers reviews and still get it for "free"). That faction is likely to be either Chaos Dwarves or Ogre Kingdoms.
Not sure what you mean about coming up with crazy stuff, they already have all the units and stuff, Chaos was one of the very fleshed out army in Warhammer. They can give them unique campaign mechanics based on their theme too.