As far as bandwidth goes, you need 32kbps of upload per player to make sure you don't bottom out. So for a hundred players you need at least 3.2Mbps of upload. Also this needs to be real, sustainable bandwidth. I know that some cable providers give you a little boost for the first few minutes of heavy usage but will eventually throttle it back down. Also [tinfoil hat] I suspect they may artificially prioritize popular speed test sites. For cpu usage, it's number of bricks * number of players. 100 players with ~5000 bricks is probably no problem, but 100 players with 100k bricks is basically impossible.
