My house was built in 1920 and I spend more on my car payment that I do on all my utilities combined. Even if you buy a house that costs a lot of heat or cool, it's at most a weekend project per room to rip down drywall or plaster, put in new/better/any insulation, and re-drywall.
That depends. In a lot of places, if you expose any wiring (aka, rip out drywall) you need to get a building permit and inspection for the work you're doing.