Stick with the i/h/e setup for now. Personally I'd get a Tanabe Super Hyper Medallion exhaust but that's my preference.

Anyway I would get a set of sticky tires and swap out your shocks and springs for performance items. That'll improve how your car handles the turns pretty significantly.

From there you can refresh your brakes with things like new rotors (plain ones are fine) and high performance pads and fluid. Braided stainless steel brake lines will help improve the feel of the pedal.