As mentioned, getting AV'ed is a good idea especially since you're so close to 18. I'd advise the wait game here, you'll find a larger selection of rifles and the classifieds will net you some good deals that will go easier on the wallet. If its M4s you're interested in, it'll be even better as almost every other gun on there is an M4 :P
Dont forget, buying from other players will usually net you some extras that you'd normally have to go out and buy anyway. Battery/charger/magazines/scopes/sights etc. Plus our retailers have access to more exquisite ones should they suit your taste.
Attending a local game and renting out a gun would be a great way to get a feel for the sport. As for gear, you can make do with outdoor clothing and a vest with pockets for magazines, but dont skimp out on certain stuff. Eye protection and boots come to mind. You dont want to compromise on those. Other stuff would be gloves, elbow/knee pads if you need them and face masks (or paintball masks, as required on certain sites).
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)