Yeah, several times when I was younger I had to move house with only what I could fit in my car or what I could carry. It forced me to really think about what possessions actually matter, and feel the benefits of how having less stuff helps free oneself from the consumerist mindset.
On another note, geothermal energy isn't feasible for most places, and building from scratch is harder than it looks ... the best thing is to repurpose what already exists to your needs and use it in the best way you can. I bought a house that had been abandoned, and it's gradually coming into shape with improvements like insulation and double glazing ... eventually I hope to have heating from a heat pump, but that's out of my price range for the moment.
And how much of that did you actually need? Why have two desks and a dining table when you can put a laptop on the table? Why have an L shaped sofa and not a compact 2 person sofa? Why have a grand piano (I'm assuming since you had a lot of space) rather than a compact electric piano?
In our first apartment we had a king size bed BTW, the space under it was great for storage and good sleep is important!