That seems like a lot of power just to run the furnace and a few lights. If it were me, I would shake it down using the actual loads, but build up to them. Start with those few lights, then add a refrigerator. After an hour or so, switch to the ECO mode and see how it handles the refrigerator. If all remains well, which it should, switch it back to full speed and introduce the load of the furnace. After an hour or so of that, switch back to ECO mode with everything you think you might want to run in an emergency connected. Change the oil somewhere between 5 hours and whatever the manual calls for, then call it a day.
Personally I use regular E10 gas with a dose of StaBil Marine 360. I've seen suggestions of race gas or premium fuel. Race gas would be ethanol free, but you get around that by treating the gas. I've been doing this for five years now with six pieces of four cycle OPE without experiencing an ethanol related problem. As for premium? These engines don't have the compression ratio to justify that; save your money!