Quarian Infiltrator gonna be any good?

No idea, they get a new skill called Tactical Scan however, so could be a good improvement.
Quarian Engineer gets Arc Grenades which'll be cool

I haven't started the multiplayer yet, Which class do you think is the easiest to start off with?

I personally think that the easiest class to begin with is either Soldier or Engineer, I'd try them all out though and see what you think, what I tend to do now I've been playing it a while is get each class to highest level (20) before promoting them (basically resetting to 1) and moving onto another class.

If you have it on Xbox I'll play with you sometime, always looking for people to play with, randoms are ok but the majority are idiots, and of my friends only one will play it with me.

Promoting puts the character back to level 1 and adds 10 levels to your N7 ranking, basically a collective ranking of all your levels. For example, I've got to level 20 and promoted enough times to get my ranking to 548.
Also once you promote a class it gives you 75 EMS points towards the war efforts in singleplayer, giving you an easier time of getting the best ending. Promoting each class gets you 75 points but only for the first time.

Fair enough, don't worry about it :P

Does the N7 rank do anything? o.O

I wish I had money to buy live -___- its the only reason i play on PSN

N7 Rank is purely for leaderboards really. I fucking love ME3's multiplayer so mine is 548 while none of my mates are above 175.
Highest in Britain is currently 6000+ and worldwide its like 7000+

I'm sort of lucky, I buy a year of XBL for £30, relatively cheap considering its normally supposed to be £40. My dad has a PS3 so I can use that if he isn't on there but I much prefer Xbox Live in all honesty.

Oh okay

Live is like $50 a year and I just don't have the cash for that lol Live is a better community. Like I used to play COD on live and its a lot harder to do well on live compared to PSN where I pretty much dominate most games

I only get my live cause I'm still in school/college at the moment, and the way it works is cause my parents earn piss all money I get £30 a week for support with education supplies.
So far over 2/3 years I've only actually used it to buy some books school wise. Otherwise its been for Xbox Live, games, a tv and a new laptop :L

Where the fuck is my singleplayer content Bioware?