Many years ago I was in Detroit Lakes, MN for the long weekend. Driving around town to get sense of the town I came across what looked like a outhouse on top of a basement. They were all covered in roll roofing running up the sides of the outhouse and it had a steel insulated door on the front. There was a wooden post which had a electrical meter attached on one corner. The post was braced really well.
There were two homes like that on the street. I stopped and spoke to a neibour who was cutting his grass and asked what the deal was. He said both homes were owned by young couples who only had so much money. They saved to buy the lots and then to put the basement in. The plan was they lived in the basements till they had saved enough money for the materials to build the houses they wanted. Beside being called "The Mole People" it was very comfortable inside.
The city first objected to it but as there were two family's doing this they let it slide.
This was back in the mid 70's
Build yours, put in the mechanicals so you can enjoy the property and build when you can.