I'd recommend the rapid assault vest from condor, you can attach some fazmags or mole style mag pouches if you find 6 - 7 mags aren't enough. I currently run 8 mags total, 6 in my vest and 2 (double stacked ) on my gun. You'll want a dump pouch (20$) and a belt to attach it to, I'd get a battle belt personally (30-50), that way you have something to attach your dump pouch and you can get a horizontal tank carrier as well and attach mags for a pistol if you decide to get one eventually.
6 mags seems to work well, I have more because I typically play outdoors and we swap ends after each game so I don't have enough paint for the second game. With 8 mags you only have 160 balls, I also carry a pistol so an extra 35 balls with 5 mags....so I hit the field with less than 200 rds on me, no big deal for indoor or smaller scale games but for large games it can be tight if you want to be on the field for any amount of time.
Also consider a sidearm. I often swap mine out in a firefight if I burn through my mag. It's faster to drop your main and grab your secondary in a pinch than swap mags...and o be honest, it's just freaking badass when You do that