You just hold a mafia game in the chat xD Days and nights last a lot shorter compared to forum games. In the chat games they only last about 3 mins in night and day lasts from whenever majority vote is reached. XD
You think about what roles you want in a game, then you think how many players/other roles would it take to balance that out. In xeno i wanted 7 blue roles and a lyncher, so i made the scum team stronger and had 21 players.