Welcome to the forum
@Deep Shore . You have a Fisher Grandma Bear Model. They were made with a top vent like yours, as well as a rear vent on some models. The easiest way to remove the rust is with a wire wheel on a drill. The doors are cast iron, the rest of the stove is plate steel. The best way to increase efficiency is to add a baffle plate inside the stove, and to use a good chimney. I recommend a stainless steel insulated class A chimney. I paint my stoves with Rutland black stove paint.
I heat my 2 story house with my Fisher stove. It is my only heat source, and I live in northern NY. I use a single door Fisher stove called the Mama Bear. I've been heating with it for 7 Winters and I wouldn't trade it for anything, not even a new stove. But that's my opinion. I know for a fact that I burn less wood than my neighbors do in their new stoves. I don't honestly know why, but it's a fact. Could be the stove, or the chimney, or the quality of wood, etc.
During power outages we can (and have) cook on our Fisher and we always have heat. We can load our Fisher at night before bedtime, and wake up to a warm house in the morning. Our stove will burn for 4 months without ever going out. My wife would kick me to the curb if I got rid of our Fisher stove.
Just my two cents worth...