Well, here's some answers to your questions about performance mods..
With the Exhaust, if you want loud and low then you can go with the Greddy PE cat-back.. It's the loudest around.. Also my ApexI World Sport cat-back it pretty loud and low too..
As for Headers, if you hold tight for a month or so I'm working with the people at Quest-Power in Japan to have something developed for my GS and if it works out I'll be selling them for the GS3's...
Lights, those greenish ones that you are talking about are factory headlights sold through Lexus on 02-03 GS's.. Now if you can deal with the light housings you have know, just add some hid's.. Philips is what I use and most people would agree that they are one of the best if not the best.. With those you have your color choice, you can get white/blueish (4100K), White with a tad of purple (6000K), and Blue (8000K).. They all look nice but the 8000K aren't as bright as the other 2...
Now with the chip, since you are putting in the WR intake I'd suggest you talk to them about getting their piggyback ecu..
For the rims, this is where your gonna love me.. I am the Eastcoast distributor for Work Wheels and I'm about to have a summer sale just for LOC members.. Take alook around the site and let me know if there's anything you like.. I have Work Rezaxx II 3pc. on my GS.. And those rims are bullet proof.. I'm not kidding..