Look on ebay for wheels, I got polished Cobra R's for $529 "Buy it NOW", there are plenty of styles, I agree with TARZAN, get some 17's, they look better on the car. Bullitts look nice on 99+ Mustangs, you can get them Silver, Dark Gray, Black, Polished or Chrome. 17 X 9 is a good size, they fill the rear wheel wells better than the 8" wide rims. I just got a new set of Nitto NT555 tires, I like them better than any I have had on my car, and I have had Goodyears, BFG's, Sumitomo's and Capitals on it before.
99+ Mustangs have a good track record, they are dependable with no real problems, hope you enjoy it!!
Oh, and welcome to Mustangworks