2. a) 18 players is the 'standard' maximum, though it can be modded to allow more. I would use the standard, though.
b.) If it's on a LAN, you're fine as long as the game can run sufficiently to play a full SP game, and there are no firewall issues.
c.) Play on Quick setting, for 3 to 4 hours. That's typically a complete game or far enough to determine the likely winner.
If you're flying people to TO, I'll join