| Budget - How much will it cost me?
If you consider playing milsim airsoft, I would recommend holding off on buying gear and doing research instead. Chances are, you will join a team and will be simulating a specific military unit in a specific role (ex: US Marine rifleman). This will require special camouflage and gear, sometimes obtained through specialized retailers. Expect to buy gear not mentioned anywhere on this site and pay premium prices for recoil weaponry and scopes.
You may also consider holding off on buying gear yourself because your team leader may be managing this to ensure consistent loadout for the team.
I would estimate paying no less than 1000$ for the gear and equipment.