What is the biggest rim size that people have fit under a 90 jetta, with out rubbing, cutting etc.?
16's should work fine which is what I'll be running come spring. 17's may have some rubbing issues depending on the weight of the car, if you have it lowered and what shocks/springs you are using. Also, it will depend on the width and offset of the wheel as well.
Depends on offset and tire size. I've got a set of 15" BBS rims, standard offset. Can't run a tire taller than 195/60R 15. Might get away with 205/50R, not sure.