I would, as a pathfinder (and end) player/gm, that you look what you need beyond the initial core book. Pick and choose. There are a TON of products for the campaign setting, which I have some experience in as a venture officer running organized play, and the firs thing I suggest for the setting (if you want to get into it) is the Inner Sea World Guide.
Then read it. Find the part of the setting you like, then pick and choose content tied into it. Do not try to buy everything all at once. If you want to get a lot of books, definitely investigate the PDF versions, which are cheaper, or shop around.
And here is the dirty 'secret'.. the PRD is everything 'core' that Paizo offers and the SRD, with a slight change to names, is pretty much EVERYTHING. So if you got net access you don't need much at all.
That being said. I always suggest you check out the content online, LOTS of sources there, and pick and choose what you need/want/desire.