I'm in the northern Arizona high desert, and the temperatures go from touching 100 on the summer to an all-time low of about -20 in the winter. I don't know what the deep ground temp is; my house isn't really deep enough to hit that. It's been sitting in the mid 60s for the last few weeks, FWIW. I considered doing the whole earth umbrella thing, but didn't follow through on it. I just have a 6" exterior concrete wall with about 2' of dirt directly on top, and progressively more dirt as you go down the sides. The house faces S/SE, and gets good solar gain through three big windows in the front wall.
For sewer, I have a professionally-installed septic system with leach field. Code here specifies a 4-person-sized septic system as minimum, so that's what I have. Overkill never hurt anyone, right? I used a composting toilet for a season while I was building, and came away with a very definite desire to never rely on one again. IMO, they suck. Maybe if you spend as much as a septic system costs you can get a good one, but I'd just as soon not have to haul my own excrement around. Flush and done is much better, IMO.
Doing this in PA, I would want to be much more careful about groundwater and seepage and leaking issues. Here in the desert, I am able to get away with kinda half-assing that stuff, because there just isn't much water around and my soil is very sandy and drains very well.