Goggles, gloves (because no one likes getting shot in the knuckles), pants then a top. When your getting on a bit and your knees and elbows can't take the punishment like they used to, then invest I'm elbow and knee pads.
As said before the companies above are all trustworthy, but to be honest you will he able to pickup a.bargain on here. Most guys take really good care of their kit before selling it on, most of the the time its almost like brand new.
As for what to buy, everything is good quality so it comes down to price and personal preference. Be warned, paintball sizes are a lot bigger than normal clothes sizes. I would say normally be an L/XL but I bought some M pants of here and there's loads of room.