Suggestion: If you want to buy ANYTHING you better go to the dealer soon becuase last time I went to the dealers 3 days before I had to leave and I wans't able to pick anything up becuase usually they don't stock any aftermarket parts due to the limited amount of space, well at least the one I went to. Also, a lot of the shops are in the boonies so you might have to have someone drive you there... some stores you should look at is Autobacs. I went to one of the Autobacs in Tokyo but they didn't have much aftermarket parts and it seemed like a cooler version of Pep Boys with all that cool Japanese cleaners, gadgets, and navigation systems. I think one of the biggest shops around is called Super Autobacs and I saw a fixed up WRX parked inside it from a picture in a Magazine.
I think if you don't have rims you should consider getting the JDM STi Rims, i think those rims are AWESOME and they should run you aobut $300-350 a piece. Make sure you can bring it back though