I've gotten the surgeon's paperwork filled out, a copy of my insurance card, my five years of weight that my PCP filled out. Should I get a letter from my PCP saying he agrees or approves or whatever the surgery...or is that something that will be needed and gotten later?

If you are trying to get this covered by insurance and they require the 6-month supervised diet, you might as well wait. Otherwise, if you are self-pay or if your insurance does not require the 6-month diet, then I would definitely do it. Every little bit helps! Good luck!