Awww..... Why don't you want to b teh 1337est sn1per evah and pwn all those noobs with your 1337 snipah skillz?
You're going about this smartly so we'll help you out with almost anything you want. I'm going to assume you've read all the FAQ's since you mentioned AV and all that.
I'm assuming since you play milsim paintball you have SOME equipment. What you should be doing right now is getting together everything you don't need to be AV'ed for. Head over to your local army surplus store or a retailer and pick up some of this stuff. You might have some of this stuff but I'll mention it anyways.
Ballistic glasses or Sealed ballistics
- if allowed by field, otherwise, low profile paintball masks are your friend so you can actually use your sights)
- Whatever pattern you like really, but keep in mind that "arctic camo" won't really work in a treed environment, and CADPAT won't work well if there's a lot of fallen trees around (the brown from the tree trunks) rather than it being full oh healthy trees and bushes.
- You may or may not have one of these. Not sure how the milsim paintball ones you use are like but check out either the gear classifieds or a place like Ebaybanned
- I have a thing for good boots. Keep your feet comfortable and all that. If you're willing to pay a little more for something thats fits better get it. Your feet will thank you. Also if you want pick up some Superfeet insoles I swear by these.
And get whatever other gear you think you'll need, don't be a gearwhore though cause then you'll have no money for a gun when it comes time for that.
NOTE you can order pretty much anything off international retailer sites EXCEPT: Guns, Metal Bodies, and magazines with visible dummy rounds (eg. G36, or Sig mags) so getting a chestrig off redwolf, ebaybanned, ehobby, war4toys, Dentrinity, UNCompany, or wherever will not get seized, it may take some time to ship out though but those stores are legit, there are many other stores I haven't listed but those are the first few that come to mind.
It's very rare we get a newbie who actually reads the FAQ's and even rarer that we get a paintballer that doesn't try to use their 999 years of experience in paintball as a bargaining chip.
Finally, if the field is secluded (eg public has no access/line of sight or whatever) and you talk to all the neighbours in the area AND inform the police department you shouldn't have a problem. Also you might want to not let any random people play at your field because I'm assuming you don't have insurance so if they get hurt you might be in a bit of trouble. That is unless you trust Joe Schmoe airsofter to not sue you. Over here there's an agreement that if you get hurt you don't be an asshole sue the field owner.