yes complete the campaign.
100
yes you have to complete the campaign then do mission select then do the bonus one
If you complete the Single Player campaign on MW2 on the 2nd difficulty you are awarded 50% completion. To gain the other 50% you have to beat the campaign on the "Hardened" and "Veteran" Difficulties.
No, But there is a spec ops type thing which is like campaign but is muliplayer.
You can't.
yes.
some guy you have to escort
No, MW2 does not have 2 player campaign. Although, it has 2 player Special Ops. Black Ops also has two player online.
no, it would not be as good.
if you collect all of them it gives you cheats in the main campaign
Nope, so far only World at War has co-op campaign.