Just to echo a few of the other posts:
1) seat time is where you will make the BIGGEST improvement. Parts are great, but until you push the limits of the stock pieces, you're really not gaining anything. To be able to push the limits, you (generic, not specific) need to get some high-performance driver's ed training. It is NOT the same as driving on the street, not even close. Unless you have a lot more seat time than most, a trained/experienced driver will KILL you in a stock car, even when you're in a fully-prepped racer... It takes some time before the car really comes into the picture in terms of overall performance.
2) Tires, tires, tires. Sticky R-comps or softer (100-140 UTQG) compound tires will out-handle any "maximum performance summer tire" on the market, all other things being equal. They make the single largest impact on the vehicle grip of all other modifications, period. Also, on the S197, the staggered tire size will induce a bit of understeer, which is actually preferable when learning to approach the limits, but will quickly become the limiting point of the car's performance. Ask me how I know...
Seriously, no matter what hardware you throw at the car, the tires will define the limit of the mechanical grip, and the level of driver ability will determine if the limit can be approached, and if so, done in a safe manner. There IS a reason that after only one weekend, the average HPDE-1 driver can increase their corner-exit speed by 25-30%...