Yes
offline firefight coop surpports online 16 players, system link 16, and 4player split screen.
Yes.
you can if you play coop campaign mode. The second player will be the arbiter
Yes, Halo 3 can be played in local co-op campaign and in local and online PvP multiplayer.
The PC version doesn't have split screen; that's only on the xbox version.
Yes...
Both players will be Master Chief.
Actually, Halo Reach will allow 4 players to play through the campaign, split screen or through Xbox Live. It's perfectly possible to play with only two or three players as well. As a side note, you can play split screen with your buddy and play with two others on Xbox Live, provided both of you have a Gold Membership.
up to 4 players if u have that many controllers but only on split screen as xbox live stopped
yes
Yes you can
Local split-screen goes up to 1-2 on campaign, it goes 1-4 on multiplayer. It goes up to 16 online.