Xbox live yes
Yes, as long as one has Xbox Live membership then he/she can play with others. You need to have Xbox Live Gold though to be able to play on multiplayer based games like Halo, COD and what not.
No you don't need to you can play with a tv remote
They stoped online play for Halo 2 back in June 2010. And you need Xbox LIVE to play halo 3, however on the new Xbox 360 u can play halo3 online for free
You cant you need gold to play online with other people.
No you don't.
Yes, you do. Without any type of membership to Xbox Live, it's known as no membership. Silver is the next level up, allowing you to do some things online such as talking to people in a private chat and seeing other people online, but not allowing to actually play online. Gold Membership (being the highest type of membership) is the fullest experience, where you can talk to people in multi-person parties, add friends to your friends list and play online on any game, at any time. There's much much more to Xbox Live than I have told you.
Nope you can play all the halo series' campaigns online and off with out any downloads
No set grade, play whenever.
You Only need 256 MB.
No, you cannot. You have to get a Gold Membership to play online.
No, you will not need to purchase a PlayStation Plus membership to play online with the PS Vita.
no... only if you want to play online matchmaking