First of all, thank you very much for the many responses. There are many good suggestions among them. I did not expect that! Before we go further into detailed planning, I am waiting to see whether the house in this form will even be approved by the district office. For this purpose, I have submitted a preliminary decision, which has already been approved by the municipality.
It is a family project. Since I am single and have no children and also exclude this possibility in the future, a 70 sqm apartment is completely sufficient for me. The other apartments are intended to be rented out and serve as an investment and retirement provision... or one apartment as a retirement residence for my parents, in case they can no longer/want not to manage their large house.
The target group is older married couples or couples without children (max. 1 child). I was thinking of rent of about 12 to 14 euros/sqm. The area is rural, between Augsburg and Munich. Many people from Munich/Augsburg have moved here in recent years. Accordingly, prices have risen. The standard land value is now 620 euros/sqm.
I now have an offer from a construction company. They would build the house for me turnkey for 950,000 euros. However, I am considering having only the shell built and awarding the rest through my own management, or putting in a lot of personal effort.
Alternatively, I had planned a semi-detached house, which would also fit better on the "small" plot. I would only need four parking spaces... However, a semi-detached house is actually much too large for me and the cost/benefit factor is also not so favorable. Let's see what happens...