You can assemable same as a Remington 870. Several videos are on YouTube.com that show how to do this.
The exact value of a Remington Sportsman 12 Magnum actually depends on a couple things. Some of these things would be the condition and age of the Magnum.
The Remington Model 12 Sportsman came in semi-auto or pump configurations, and were made from 1984-1986 (vintage?). The auto is booked at $300 in 100% condition and $150 in 60%. The pump from $275 to 140. (Add 10% if it has Rem-chokes).
You contact Remington customer service, and ask for an owner's manual for your rifle. Then read and follow the manual.
Don't know for sure which you mean... Sportsman 1930-1947 Sportsman 48 1948-1968 Sportsman 58 1956-1963
50-200 usd
Remington's website has a history section that you can look at.
About 275 in good condition
Your question answers itself.
Go to Remington's web site and look under their Firearms History section.
Should be on the action, Sportsman could be the 48 or 58 semi auto. Sportsman models have little parts left so try not to break any.
If you look closely, I think it's a Sportsman 48 instead. Anywhere from $100-$300 depending on condition and options.
Impossible to answer.