At 15 just get it in good running condition and forget anything at all about turboing it.
I have worked in the performance automotive realm for years now and currently own 3 fox bodies. One is a stock 5.0 and another is having a 6.0l LQ9 chevy engine being built for it right now. A fox Mustang with headers and a e303 cam will be great for you to have and enjoy for along time. It is already becoming a classic so don't let the nay sayers offend you.
If you want to have some more fun with it put a 3:73 ring and pinion in it and let that be it until you get out of high school and college. Then worry about the rest.
As for changing to speed density in stead of MAF don't waste your time or money.
exactuly i already took it up to get a quote for paint on it gana get that done over winter can drive the damn car in winter anyway the only other thing im gana do for performece is a cat back system and a new intake or a ram air kit