Yep, best advice already given.
Thing is, in paintball, you will use way different tactics than you would in an actual military op, so watch out for this. This is why so many military folks LOSE all the time in paintball....the concept of sacrificing players is alien to their training, yet an essential element sometimes in achieving a paintball victory.
So, you and all other players would have to have to treat it differently than typical paintball...and more as a military sim. I used to be into it pretty heavily, even doing it at National Guard training bases for urban combat, etc. (what fun)...but not so much anymore. Highly recommended though.
I think Airsoft is probably a lot more realistic for milsim though. Mostly because the good quality guns can have the same weight and feel as the real thing. Whereas paintball markers are MUCH heavier.