1) Imperial Cutlery Company. As far as I know, they've been out of business for quite a while. They generally made inexpensive knives.
2) Prov RI USA means Providence (the city) Rhode Island (the state) United States of America (the country) indicating where the knife was made.
3) Hard to say, but probably 1095 carbon steel if it has rusted. Imperial used both carbon steel and stainless in their knives.
4) Flitz Metal Polish and a Scotchbrite pad does a pretty good job without removing too much steel. If the blade is badly rusted, automotive sandpaper may be faster at the cost of removing more steel from the blade.