You bet, you can sign up anytime up until the course starts

and no, there's no real limit on the number of students. The class discussions are held on a private forum (similar to these, but limited to course students only), so people can tune in and out when they like, and choose their own study hours.
The only books you'll need for the course are an ephemeris and table of houses ... you can pick those up in advance if you want, but we won't actually need them in class until lesson six, around the end of October.
Love,
Greg