How many Players can play at maximum?

[tempest]

1) Theoretically, one server can host up to 256 players (AFAIK you can set the max. player number in the maprot.cfg) . However, if you want your server to register on the online masterserver (which is not necessary for a LAN server), it must have no more than 20 slots, as JGAN said.
2) As far as we can see today, AC will always remain free.
3) No, you can't play with bots in multiplayer.
4) max. 2 teams, as everywhere