Yes, both referee assistants can wear a cap during a match, as the sun may get in their eyes and not see a crucial part of a game.
Referees can wear Blue, Red, Green, Gold (yellow), or Black. The color choice depends on the kits being worn by the teams in a specific match because the referee must be easily distinguishable.
Yes as long as they are not hard but not on your wrists only on your head.
You are allowed to wear tennis shoes or sneakers at the referee's discretion.
Sometimes you can just wear a short with a shirt and play a normal football [soccer] match. I think you should not wear trousers for matches because it could get durty. But if you are playing a match in a football team wear a football [soccer] shirt,long socks,shimpads,football[soccer] shoes and shorts.
So he can be distinguished from the rest of his players by, the players on the pitch, the referee and officials and the fans.
Indeed, Referee or any Sport's person can wear Prescription glasses
The second watch is a backup. As a referee I have had 3 watches fail on me during matches. One had an electrical problem due to water infusing the case and the others had their bands snap. In general the assistant referees and 4th official are also keeping time.
Yes it is required in every match. Before the match the referee inspects the gears of all the players making sure they wear the right gears and protections. Every player must wear spiked shoes, shin guards and goal keepers must have gloves. Also during the inspection the referee checks all jerseys are tucked in for the safety of the players.