Since I'm such a pro i'll answer your questions 1st.
1: I am super into performance. The two main things I would get first are an Intake (Injen CAI, Frankencar Hybrid...etc.). Personally I like frankencar, it sounds like a mad beast when your WOT and they are really good down there. Steve from frankencar is really nice and everything fits well. The other big mod is a Ypipe. I have bought from budget twice and its about 180$ shipped to your door and I got it in 6 days my 2nd time ordering it.
Those are the two basic perf. mods. If you want to get serious you can get a basic nitrous kit for about 400-600 used or new with some accesories.
2: I can't really help you with looks, I've never done that much. You can buy those diamond cut clear corners which look sharp and also shave the emblem and words off your trunk.
Thats all I really got right now.
Check out maxima.org and go to parts for sale, sometimes you can get some good deals and everyone is really nice there. I think someone is selling a frankencar intake for 100$shipped.
For my future plans I'm set on a specific goal and thats hitting low 14's or high 13's.
I only got intake,ypipe,and catback but I plan to get a UDP, hopefuly MEVI and nitrous in the near future.
Hope this helps,
=Scott