It doesn't but it does have downloadable content.
No. That's a single player game.
No
Mass Effect 3 campaign is only single player in itself. You can however play online with other people by using it's multiplayer functions.
If you want to, and you're into video games. Try reading a few online reviews about it.
Yes.
This is up to you. But, my opinion is that you should definitely play ME1 first. You get a better feel on the Mass Effect Universe, and you will be more attached to the game, and will enjoy ME2 a lot more. Mass Effect 1 is a great game, as is Mass Effect 2, but if you have the time and the money, play ME1 first.
There is neither a co-op mode or online mode for Mass Effect 2
Yes. Mass effect one is available on the play station three.
There is no (useful) official info on Mass Effect 3 yet as ME2 only came out earlier this year. Yes there is, in fact, if you get the Mass Effect 3 demo, there will be automatic Gold Xbox Live to allow you to play online without paying for it. It ends March 5th though.
If you don't import a save game from Mass Effect, you will automatically choose the character of the opposite gender to survive. If you play Mass Effect first, though, you can choose if you want Ashley or Kaidan to survive. So to play Mass Effect 2 as a female and with Ashley alive, you would have to play Mass Effect and let Kaidan die on Virmire.
You won't be able to import your save game from ME1.