I did my first autocross in 1984. Fook I'm old.
100 mph is too much for a novice autocross person. In the old days it was called Solo 1 and required more safety equipement than a stock/as delivered car. I wouldn't be comfortable in a car w/out safety stuff at those speeds.
I posted somewhere else
the Nationals course from in-car (not me). They were very good courses.