Wiltshire Arms was a trade used by J. Stevens on shotguns made by them. Value will depend on exact model and condition, but is not great- typically $50-$100
Impossible to answer without a detailed description of all markings, condition, finish, type of action, barrel length, caliber/gauge, stock, engraving, sights, etc..
dude not trying to be mean, but what gun are you talking about dude! if i had a gun i could tell u how much its worth, and also you could do it yourself!