Assuming that you have a standard grade winchester model 12 shotgun without a cutts compensator,and it is in good(80%) original condition? The value would be 375 dollars.
Do a google search for "Winchester Model 12".
A million dollars. ;)
Winchester Model 12 shotguns in good condition can fetch prices from $500 up. 12 gauge is the most sought after size.
Impossible to answer without a detailed description
The Winchester Model 12 was never sold under the JC Higgins name.