Best left to a trained gunsmith
The markings.
yes
500$
I would start my search at Smith and Wesson first.
100-300 usd
50- 325 USD or so
You must call S&W for a correct answer.
You should call S&W to get the correct answer from them.
You will have to find someone who specializes in air gun repair.
100-3000 depending on specifics
About 3 percent or so.
Looks like any other pump shotgun. Usually one or two on the auction sites with pictures.