yes you could with another person playing on the same xbox 360
yes
yes you can. on everything i guess.
offline firefight coop surpports online 16 players, system link 16, and 4player split screen.
Yes, Halo 3: ODST will feature offline cooperative Firefight mode.
Up to 16 with system-link, but only 4 with split screen.
play with two people by playing split screen
You can have more you can have up to 4
Inheritor.
To get credits in Halo: Reach with a silver, or offline account, you need to play offline Campaign, Forge mode, or local Custom Games.
you don't.
no you cant
The PC version doesn't have split screen; that's only on the xbox version.