You can get away with running larger tires without traction roll problems. The track is easy on tires, so you can run small diameter, although there are some bumps to consider. Just bring what you have, you will have fun.
The race weekends seem to start late. I was there a few weeks ago for a race, and nobody showed up until 10:30, which pretty much sucks. There was no race that weekend, but good practice. A friend drove 150+ miles to race that weekend, was there at 8:30, and bailed because nobody was there. Check first.