Its probably going to be no more than 3mm, probably less, before you've effectively created a dangerous situation. Don't quote me on the 3mm. But without extended studs, you won't be able to grab enough threads with the nuts so that the wheels won't fall off.
I'd suggest selling the wheels and getting wheels with an offset that is more appropriate.
I've not changed the studs on these cars, but its not exactly an easy job on the other cars I've changes them on. May even require wheel bearing removal and a hydraulic press to press the studs into the hub, and a new wheel bearing because normally they get destroyed when you remove them. The extended studs themselves are going to run $100+, wheel bearings a few hundred bucks, if you aren't going to do the work yourself, I'd guess it would cost at least $300 for labor, probably a lot more, then whatever the spacers cost on top of all that. Also keep in mind that running high offset wheels, which is essentially what you'd be doing, can cause the already weak bearings on these cars to fail.
Honestly, there are a lot of reasons not to use spacers.
Personally, I'd just sell whatever wheels you have and get wheels that are the size and offset that you are going for.
Wow.honestly i thought its much easier then that.so if i want to change the rims should i just look at 17x7 5x100? i would rather get the rims with nice tires.is ebay a good place to look? i wanted to put gold sti rims but i know there is a lot of problems with them.
You can put larger wheels on your car. Iff you were to put 17x7's with a more agressive offset so that they stuck out, that would put stress on the wheel bearings. Its best to get a larger wheel with an offset that is neutral, so that it sits where you want it and doesn't eat up your wheel bearings. You can easily go to about 17x8.5 +30 without any issues. Perhaps even 18x8.5 +30. The tire size is going to be a bigger issues. A good place to look for wheels is WHEELDUDE.COM You can just click the links and it will show you a bunch of popular wheels that will fit on your car, and you can even buy tires with them at this site.