Ok, this is not going to sound good, but I'm trying to save you some headaches and other issues. 1) You're not even 18 yet. 2) This is your first car. 3) An ITR is a very performance oriented car.

An ITR is well above your driving abilities and it will take quite a while before you "outgrow" it and need to modify it in any way. In stock form, it's fast, fun, and handles really well. My suggestion would be to learn all aspects of the car as it is before you start doing stuff to it. If you truly want to see what the car can do, sign up to take HPDE courses or try some autox events. In the hands of a very capable driver, a stock ITR can be very fast. I've seen cars with stock suspensions and revalved shocks absolutely obliterate other cars on a race course that have $5000+ suspensions. It's a car that rewards the driver and the beter you can drive, the faster the car.

Invest the $10,000 and you'll thank me later. And keep in mind this is coming from someone who spent well over that amount on a car and still wasn't happy with the end result because I still wanted more.