I am in the baby-step stages of doing something similar to what you are talking about, so don't take this as a blast, but...
From the questions you are asking, it sounds to me like you are not ready for such a big undertaking. If you had (have?) booked smaller acts, you would already know how to cold-call their people, and would have some idea what to pay. Your (apparent) lack of experience is going to come through when you talk to people, and that opens the door to them taking advantage of you. I just don't see how you can get enough "practice" here, so that you don't sound like the noob you fear sounding like. Also, problems will ALWAYS come up- you run the great risk of having what should have been a surmountable problem, overwhelming you and your resources, and threatening the entire deal. You ARE a noob at this, and it sounds like you are SERIOUSLY over-reaching. You could fall flat on your face, and it will hurt- I'd hate to see you get discouraged and decide the whole thing is not for you.
I am working sound at a music and art festival this weekend in Pine Lake, GA. Great little town near Atlanta- 700 people are registered to vote for Pine Lake's mayor, city councel.
http://www.pinelakega.com/ The man who was organizer last year had some grand ideas which sounded good and probably would have been great for the festival- eventually. Unfortunately, he is not involved this year. I am not privy to the reasons, but I suspect it is mainly due to him burning himself out IN ONE YEAR. He may have done better, both for the community and for himself, had he taken it down a notch or two, last year.
The event I hope to get going will start small (actually, has already started) and hopefully grow, year to year. That way, I learn as it grows, and hopefully the problems that come up will not overwhelm me.
You gotta crawl before you walk, walk before you run...