Before you order anything read the rulebook. I used to be car chief for an ITS BMW 325is. There are alot of things in the rulebook that are not allowed and you will get caught and they don't like allowing cheaters to race. I know of several friends that were banned for cheating. Pick a class you plan on racing in and read the rule book. Touring class will be your best idea. A 99 si will either be ranked in ITA or ITS. These classes are very specific on what you can and can't do. First you should focus on the safety stuff like a cage, seat and general car prep. Then move on to suspension and tires. Springs/shocks are pretty much open as long as you don't try to run something like Motons w/ an external resevior. Depending on the car you may not be able to use aftermarket sway/strut bars, camber kits are definitely allowed though.