I'm pretty much in agreement with DonC. I'll add two things. First, you'll get a lot more track time per dollar at open track events than at autocross events. Second, hard driving will reveal the weakest mechanical part of your car. When you fix that, you'll reveal the second weakest part. And so on. Some of the weak links are only frustrating (e.g., carburetor flooding). Some of them are quite expensive (e.g., engine failure due to
oil starvation). And some of them can be terrifying (e.g., overheated brake fluid). Do your homework before you start and save yourself some aggravation at the track.