Well, sounds like your going to put a significant load on the stove in time.. Things to remember about a gasser is it burns half the wood, no smoke, no ashes. If you get a quality gasser you do have to clean the heat tubes with a brush every few weeks, folks say they have the same amount of time in maintenance as they do with a regular boiler because with a regular boiler there taking out ashes, no ashes in a gasser, it burns them.
So when your talking about heating around 5000-6000 sq ft, you've got to make a good decision. My personal favorite gassifiction units are empyre and portage and main. When it comes to standar or conventional boilers just avoid small new pop up companies and go with s reputable brand.