Homes in Hokkaido area, where it gets quite cold in winter, have good insulation. If one is building a custom house in Japan from construction company that does pre-fab, ask to see the catalog for houses in Hokkaido. It will have features such as double paned windows and venting systems with heat exchangers. I'm the only one in the neighborhood with the heat exchanger setup.
Regarding central air versus having a compressor for each room. My previous house in the same area had central air and in hindsight, it wasn't an economical choice. It made all the rooms drafty and we were constantly fighting with low humidity. The current house has it's own compressor for each room and along with the ventilation provided by the heat exchanger, just running two units downstairs is enough for the whole house.