wow, that must be some glass!
Have you seen any of the marketing pics of those nice pellet inserts? they look divinely tranquil, to me...
Do you have lots of power failures? Its not really a concern, at my house. in 14 years, the longest outage we've had has been 8 hours. In general, any outages are rare. I was starting to get concerned during that one long outage...and the house was getting uncomfortably cold, so I turned on the burners on my propane-powered kitchen range, not expecting to get much. I had to turn them off in under an hour; the house was too warm! (gee, no wonder it gets so hot in the house on xmas day...about the only day we ever do alot of cooking). anyway, I don't think its a major concern (at my house), and you can use a battery backup, in a pinch.
that fireplace is probably a net loss, even when you are burning in it. It makes the area right near it "feel" warm, from the radiant heat...in exchange for sucking all the other heated air in the house up the chimney. they should all be labeled, "for entertainment purposes, only". LOL!
From reading here, and talking to others IRL that I know, with similar sized houses, I expect that a pellet stove of that size will heat the whole house. My friends run their furnaces only on the very coldest of days...like "0" degrees. My house is the same size, and better insulated. I do have 6" walls, modern construction, etc.
I can tell you from personal experience that I can cool the entire first floor of the house with a single room air conditioner. (I think its 12k btus...about as big as you can get without needing a 220 outlet). My floor plan is a bit more "open", and it is cooler near the unit itself, but a ceiling fan keeps things circulated pretty well. The a/c unit is in the equivalent spot as your "LR" front windows; If you're sitting over near where your tv is (in my house), it can feel a little bit warm there, without the ceiling fan running. with it running, its fine. I don't know if we can draw any conclusions from that...comparing a single "zone" type cooling unit to a "zone" type heating unit. So..."fwiw".