Mark CMG
Creative Mountain Games
I like to have the whole Pathfinder AP before I start running, but I definitely don't read the whole thing (terrible, I know).I generally skim the book (eg book 1) before starting, and try to read the chapter within that book in reasonable detail. From what I've found, an hour spent reading material likely to be used next session is vastly more useful than an hour spent reading stuff 5 books away.
Are the PF APs you have run written in such a way that you know all you need to know before running part one?