For posting:
- invitations to games (you can also use the New Game menu)
- information about upcoming tournaments
- discussion of games (please limit this to completed games or discussion on how a game has arrived at a certain position ... speculation on who has an advantage or the benefits of potential moves is not permitted)
- links to interesting related sites (non-promotional)
Theoretically - a lot, but that's just like saying you need 9 queens in regular chess to account for all the possible conversions. In practice it's rare to see more than 4 knights bishops or rooks of one colour, but say you need 8 of each, so you can sell more pieces :)