If you come out to a good long milsim game most of it will be the "hide n seak" type of thing. I personnaly play the sniper roll most days and rarely fire a shot on those days (unless i screw up lol).
Watch the events section and get out to a game or two with the local guys here in the gta. Alot of the folks we play with are current or retired CF and LE guys and they are a tonne of fun to play with and learn from cause lets face it they should and do know their shit.
As far as upgrading ill also say aside from maybe a beter hop up rubber and maybe an inner barrel there isnt really a need to open up gearboxes and such untill somethin fails and needs replacing and by the time that happens youll have an idea on where if anywhere youd like to improve the gun.
As for the FNC get age verified and gun info such as where to fimd one will come to you easily but we dont share such info till we are sure your an adult ( not that i doubt you are just the lil system our community has in place sort of self policing if you will) but i do know G&G and Star make an FNC aeg not surd if anyone else does.
GandG for your viewing enjoyment lol