I may get bigger rims soon (GT500 take-offs), but they have a different offset from what I have right now (50 vs 45).

How bad would this affect my alignment/handling on the car? Please let me know.

 

I'm running the same size (18 x 9.5 with 45 MM offset) Steeda Ultra-lite wheels with no problems. Right now they have 255/45/18 snow tires on them and there are no problems with the car lowered using Steeda Competition springs. In the summer I run 285/40/18 tires on the same rims and only experience slight rubbing at the front on full lock,i.e. while parking.