3 Mafia 3 Power Roles 6 Citizens sounds alright, there's a lot of Citizens but generally the town has an advantage at those sort of numbers so it makes sense to not give town an additional power role!
Sheriff and Doctor are pretty standard power roles to have in a game, as for the third PR we probably shouldn't discuss that in public!
http://quicktopic.com/ could be good for night chats/observer chats etc.