Depends on your goals but one could get the Z3 kit and be happy with it, it has had some good results. The cartuning kit is not crap either, I just wouldn't buy it brand new.

Your tranny will hold up for a while if you get this and don't drive like a jackass:
Z3 turbo kit
42.5# inj.
DIY intercooler

That should be an easy 300whp and up if you do some tuning...