Some of the levels you have to get the DLCs but most of them should already be on the game.
There are 55 levels in multiplayer.
Unfortunately, you can't change any of the settings in Black Ops multiplayer.
In Call of Duty: Black Ops, to go on multiplayer you have to go to multiplayer on the menu that says: CAMPAIGN MULTIPLAYER ZOMBIES OPTIONS
Yes.
Simply go to the black ops multiplayer settings and disable the aim assist
in black ops multiplayer, everything's unlocked already.
Online Xbox 360 play is not free and the online multiplayer mode of Black Ops is the only format for multiplayer
Yes. Both modes are one game. Black Ops 2 includes a Singleplayer campaign, a Multiplayer, and Zombies!
No
Black-ops will have an offline version of the multiplayer, with AI opposition. Also you will be able to level up as if you were online =)
Don't know about the game itself, but 70levels to 1prestige, and you can go to prestige 15 on multiplayer
50, but you can prestige after you complete the level 50 as seen in previous Call of dutys, there are 15 prestige levels on call of duty black ops, so basicly you can level up in this game 750 times