A set of hypercos goes for what, $200? Get a set of Eibach ERS for that much and get a set of eBay coilovers for $50 and toss the springs, just use the threaded collars and the ring perches. You'll have the same thing as a set of GC's but you'll have saved yourself $150 and only be a few bucks over a set of Hypercoils. I have GC/AGX as well and like it just fine, although If you're going to do mostly street driving I'd suggest you get a slightly softer spring rate than the typical 300/200. If you end up autucrossing or track racing a lot later on another set of springs for track use won't put you back more than $200 and changing them out for a weekend of racing won't be terribly time consuming or difficult. As for the wheels, I'd go with 16's.