I'd go either Geo 2 or DM12. You will save almost $200 just buying the pops asa separately. The DM will shoot smoother, more efficient, but will require more frequent maintenance, and it lacks an LCD board. Between these you can't go wrong for those prices.
A $500 marker is relative as well, $1300 guns like the NT11 can be found easily for $500 on BST forums. If we're talking $500 brand new markers then the only things I can see a more expensive marker giving you is a higher commitment to the sport, more "luxurious" features, and larger testes.
It may not be a reg leak, my cousin just bought a G4 and out of the box the macro line was leaking next to the regulator. It seemed DP used a rough edged instrument to cut the macro line causing it to leak. Check ur macro line out and see if its a nice smooth straight cut.
Unless you're using first strike rounds there really isn't a point to "camouflage" with your surroundings. Most of your shots will be within 60 feet and its pretty easy to pick up any colour of clothing at that range. I would suggest a speedball marker because of its versatility but I would not recommend the NT.