Since this is your first sports car, I would suggest that the first thing you do before spending money on add ons should be to "tighten the nut" behind the wheel
. What I mean is that you should investigate performance driving classes in your area. A few sessions with a competent instructor on a track will teach you how to get the most out of your car and more importantly will show you the safe ways to wring all of the performance from your Z that you can. Check out SCCA or other sanctioning bodies where you live. It won't cost you that much and it will surely be worth whatever you pay for it.
AZ Roadster