Well, there are two choices in coal. Stokers are nice, burn the smaller sized coal. (I do not have this type of stove, so I am not the expert). The other type are the hand feeds, depending on what kind you buy, you can burn both wood and coal. I typically burn wood in the start and then the end of the heating season, a good coal fire sometimes is too much for a warmer night, where as a wood fire can be just burned over night and then easily burned out. Hand fires burn pea, nut and stove coal.
Regardless of which kind you go with, your stove shold have enough btu's to heat your house. You stated that you have 1500 sq ft. and have average insultaton and double pane windows, I would say, 30-45 btu's per sq feet, so 45,000 - 67,500 btu's. I would opt to always go bigger than needed.
Also, stokers typically have a better blower systems, where as hand fires have more of a radiant heat, but most do have blowers.
Hopefully this helps and you are not still totally confused.