+1 for JRH. Good folks who sell solid kit. They also USE this stuff quite extensively as well. Ask them about it, they'll be glad to help.
Man this is so easy to go down the rabbit hole. It is so tempting to get all the latest and greatest stuff versus finding a level of acceptable performance, and maybe a little bit to grow into.
I think your biggest purchase is the device itself, which you are making a good choice on. A really good gen III -14. You could get gen II+ or you could get the newer WP tubes. This is a solid middle ground.
Next would be your helmet set up. At a minimum, you can get a good bump helmet, which allows you to mount the device and accessories you probably want. I'd go Ops Core here. If you want to go ballistic, then the choice is weight versus price. You can get 3-4 lb helmets (Revision A3) in the 500.- range, or 1-2 lb helmets (Crye, Ops Core) in the 1K range. If you have the budget this does make a huge difference in comfort.
Helmet accessories. Hoo boy. You get a lot of different advice here. For a good -14 set up, my opinion is an Ops Core VAS shroud, Rhino II, and J-arm (modified ball detent) is a solid choice.
IR illum and laser. Lots of choices here as well. A good DBAL gives you both pointer and illum. Add in a good switch and you're GTG.
So with your budget, what to do. A good PVS14-17. Crye helmet, VAS shroud, Rhino II, J-arm. DBAL A3 with TAPS prog switch. This will just squeak you in around 5K. If you needed to trim that a little, I'd go with an OTAL and TORCH (or SF Vampire) with TAPS, but keep the lighter helmet.