Yeah,congrats. All you really need to do is get a copy of the newish guide to the Main and have GPS going so you don't blow by pictographs,ect. It's got tons of great beta and is pretty well done.
If your group is small then try to get the camp at Chamberlain Creek. Favorite camp site.
FWIW, the fishing sucks by and large but a great float.
Last 20 miles at lower water...not much current so prepare to row if you want to get anywhere.
My bro put together a slide show deal of our trip in Sept '05 if you want a little Main porn.