Old gun catalogs and magazines.
Blue Book of Gun Values
National Firearms Company was a trade name used by Hopkins & Allen @ 1900.
Unknown.
It will be stamped into the action (the cylindrical part that encloses the bolt)
50-350 usd
Try the Blue Book of Gun Values
Low cost European rifle.
Any other markings? Is it a bolt action?
The NRA website has the information you need.
Sorry- just not possible to answer that- way too many possibles. It is likely a military rifle, since many of those had the year of manufacture stamped on them. It COULD be a Mauser or a Moisin-Nagant rifle, but without a LOT more information, we can't even guess.
The National Rifle Assocaition is a good place to go to for information.
Blue Book of Gun Values, old gun catalogs