Gears and Nitrous ?'s

I'm looking to start modding my car and I want to do gears first. I don't want anything too extreme. The other question I have is Nitrous. What systems do most of you guys have? I was looking into the N.O.S F.I kit.

Thanks in advance.

With nitrous most guys run 3.73 and a posi or LSD.

Another stupid ?

How many bolt and inch rear end does my car have?