All that sounds fine, but here's the order I'd attack with
tires are certainly where you want to start...nothing makes more of a difference than the right tires...and if you are going STS, it is indeed hard to beat Azenis
After that, suspension...what you do here depends a lot on what you're willing to deal with on the street.
After that, little things like intake and exhaust for a bit more power.
I'd worry about brake pads last (unless you're oem's need replacing anyway)...the stock brakes are excellent...some other pads may give you quicker bite and better modulation, but tires/suspension are head/shoulders above as difference makers.
And I'd scratch the body kit, too...probably just extra weight (the enemy) and more surface on which to get cone marks.
Head to the autocross forum if you want to get into more specifics.
Bryan