I'm signed up for Level II and III on the same dates. I did level I at Watkins Glen a couple years ago and got a ton out of the school. When I took the course it was only my second track day. I've read the book but as long as I apply the lessons on the track I stay consistant and smooth. I don't ride as much as I would like to, infact I only ride on the track which is turning into about 4 times a year. But I remain in the advanced group and hold my own every track day. I can't wait to see what the next two levels will teach me.
IMO, You've made the right choice in wanting to learn and you won't regret learning from CSS.