yes.
You can play first strike maps offline in both the split screen and XBOX Live -> Combat training lobbies. (Though for combat training, you'd still need to be online.)
No everything is free on split screen offline.
Both.
Yes, you can. You can play the campaign offline and against friends in split-screen mode.
no
The Annihilation map pack probably will work in split screen mode.
yes with in the 360 it has split-screen
Yes
yes
You can only play split screen on World at War if you are playing offline, and under the "Split-Screen" mode. This can be found in the co-op campaign, zombies, and multiplayer modes.
offline firefight coop surpports online 16 players, system link 16, and 4player split screen.
Unfortunately, you cannot play split-screen on Dead Island. However, there is online co-op, system link/lan, and of course.. solo!