1) All hosts will chrono your gun before a game. You can also buy one for yourself.
2)It really depends on the fields limits. They will likely be ok for the large field games that run 400~420 FPS limits, but they will likely need to have a spring swap for use in CQB @ 350 FPS. Any gun doc can do a spring swap for you, its a cheap and very quick operation.
3) Any boots that you find comfortable and have good ankle support will do.
Barrel plugs do not work for airsoft, they are not make in the right size. You will need to get a barrel condom. They can be found at any paintball shop. They are an over caution for people who don't know how to follow safety rules.