I'm not sure of the value of your particular shotgun, of course, but a left-handed Remington 1100 just sold at gunbroker.com for $575. I'd be very interested in purchasing a left-handed 1100. Are you selling one?
In order to answer this question you need to specify the model number. Open the cylinder and look in the crane. you will see a model # above the gun's serial number. 64-3
Depends on condition, vent rib or no rib, etc. $150-$250. firstname.lastname@example.org
If you want factory specs, look in a reloading manual. If you want reloading tricks, try this. 1st: close bolt on empty chamber. 2nd: insert cleaning rod with blunt tip into muzzle and stop when it contacts bolt face. 3rd: mark cleaning rod with a fine pen at muzzle end. 4th: remove cleaning rod and bolt. 5th: with muzzle down, drop bullet, point first, down chamber. 6th: Gently insert cleaning rod into muzzle until it contacts bullet and mark the cleaning rod again. 7th: measure/mic distance between two lines on cleaning rod and subtract .010. That should be the most ideal overall length. That's the length of factory loaded cartridges. And as for the method given above - why not just measure the cartridge instead of measuring the difference between the barrel with and without the cartridge in the chamber?