No on AUs, at least presently. We're considering opening the game to OCs at some point, but we wanted to leave that up to the player base... once we have a player base.

Regarding previous game CR, you're definitely allowed to reference it and break the 4th wall from time to time. We're fine with your character remembering previous game CR, but making references to it to other characters should require that player's permission; it's a little bit like canon puncturing.