Congrats! Although you mentioned some of the "best cars". That's an incorrect statement. It' sbaout the driver. I good driver should be able to take a Cavalier or Corolla and outdrive a guy driving a Mustang GT.
To learn more about driving check out:
http://www.springmountainmotorsports.com/
I took both the 1st Level and got back from the 2nd Level class in June. You'll learn braking, hand/seat position, heel/toe shifting, and learn to hit your apex. Hitting your apexs is a focus of the course. You'll hear "You missed your apex" through your headset more times than you care to remember. But if you hit your apexes, the reward is, you'll go fast.
Great class! I apply many principles in daily driving in my '02 Z28. I'm currently looking for a used C5 Z06.
The next step from autocross, is road course. There might be a few around where you live. Check it out. Enjoy braking, downshifting and turning to the right.
The Key? Have Fun!