Go with 6 cords till you know what you need (next year) imho. You get much worse winters there than we do here, I heat 700sq ft of not badly insulated house, burn 7-8 months of the year, about 3 cords + -, always nice to not run out of wood though. You are heating two stories and that is a consideration, as well using an insert, which in my limited experience, are much less effiecient than a free-standing air-tight. I lived in a rancher for a while that had an old insert, about 1400sq ft, it was such a pig we sealed up the fireplace and ran a pipe through it out the chimney with a small airtight set up on tiles and blocks out front of it, huge, huge difference, half the wood and we were warm (and cooked on it frequently too, bonus), we did need a couple of fans to kick the air around though but considering the old oil furnace in the basement ended up under water it was hardly a tough decision
Bottom line is, if your house is well insulated and not leaking like the Titanic, double or triple paned windows, insulated doors, gap seals, etc etc., you'll fair far better than trying to heat a 50's era pos. Do remember though that fire takes oxygen and it has to come from somewhere, iow don't burn in an airtight building unless you figure out what y'all gonna breathe, the fire too. Of course, you will find when reading around here, the types of wood you burn (and extent of seasoning), is a big variable as well. Hm, run out of thoughts for the moment, ciao.
My 0.02$ worth fer the evening,
Welcome and
Serge