Skip headers, everyone is going back to stock.
8" rims are best both for STU and BSP without going crazy on price and width. STU is limited to 245s.
STU is basically as expensive as TSP and TSP is way more fun with some extra
BOOST!!!
Falken Azenis 615s rock at the track and at autocross and are way faster than at least MikeK's RE01s.
Race rubber is over rated! You will learn to drive better much faster on Street Tires. Heck, the same is more or less true for suspension as well unless you drive a Caddy.
The worse your car, the more you have to drive to go fast.
If you are ready to go beyond AS, probably the first step is suspension and then an AP. I think TEIN Flexes are still teh way to go.