Just a suggestion, you might want to check out
www.ccevents.com this is the mopar series we run and it is setup great. it runs a race a month and is spread out over 5 tracks in 3 states. None of the tracks are over about a 5 hour drive. The event has a great car count at all the events. I have heard that the norwalk event this year is expecting over 500 cars. Maybe it can give you some ideas on how to setup your own series.