I'm not that much further north than you and I know our well water is definitely less than 40 df, especially in the winter. I suspect your "backup" heat is coming on more often than you think. Our first winter I had the baseboard heaters set to come on about 64df and turns out they would kick on before the stove stopped carrying the load due to the thermostat being on the other side of the room, behind a TV. It was only an hour or so a day, but it added up. I turned off the power to the heaters and thermostat and have noticed a reduction in use between our first winter and second winter. I actually never go around to putting them back in, especially since we never go anywhere.We're a family of 4 with the kids only being 5 and 3 so the bathing time is pretty standard. They get the usual and we get whatever we can whenever we can lol.
The primary heat system is a heat pump with auxiliary electric heat. The main reason I decided to go wood was to avoid using it. Ive had it set to 60 since its been cold and I've never seen the thermostat go below 62. With the stove running on a cold day it's usually 68-72 in the far rooms and 72-78 close by.
The lights are all LED inside so those don't concern me much but thats interesting about the water heater...that never crossed my mind. We just had it replaced about 3 months ago. Its just a basic AO Smith model, nothing fancy. But it is fairly cold in the basement as the stove is on the first floor. Maybe its chugging to keep the water warm? We have a well so its definitely cold water.