Initial floor plan on graph paper: slope, basement + 2 floors.

And for [doch wichtig]: The company can Hang.

Thank you! Flooring is included at 30 euros/m2 for 30x60cm tiles and 90 euros/m2 for parquet. So far, we are sure that we will stick with 30x60cm.

Sounds reasonable. I have already ordered the parquet for us and will lay it myself. Our house probably has significantly less wall/ceiling surface due to the slants and especially the missing hallway as the house entrance in the basement, and at 30€ gross per square meter for painter's fleece, it really adds up. You should best calculate around 15-20k€ for the painter. Given the architecture, I don’t expect it to be textured wallpaper.

I am really scared of that

With the ground, there are really only two things that can get expensive: rock and water. Both can be fairly well ruled out with a soil report. If it can't be ruled out, you have to set aside an extra budget. So have a report made; usually the fear is unfounded. With us, we knew in advance that we could hit rock, and we did. Money was set aside, so no problem. Of course, I would have preferred to keep the money.