Building a single-family house with/without a basement on a small plot

How high is the groundwater level where you are? What kind of soil do you have (gravel, clay...)?

The soil survey is still pending, but for the development of the area one of the boreholes was carried out 15m away from our site:
Groundwater at 2m depth, there is a lot of clay in the soil as well. In any case, not very permeable.

Which country is yours, then? I couldn't quickly find anything with 9x9m. If those are really the max. exterior dimensions, I would probably build with a basement if it's financially feasible. But I still have doubts about the dimensions.

Your rooms are partly unusable. Too narrow.

Do you mean on the upper floor?

Basically safely doable without a basement with 150-160 m2. The ground floor technology would inevitably also be storage space with this plan, plan space for washing machine/dryer upstairs. Keep garden stuff compact. I think no one can take the decision price/comfort away from you. Deciding early is of course sensible for further planning. Just play through everyday life.

Which is your country? Couldn’t find anything quickly about 9x9m.
If those are really the max. outer dimensions, I would probably build with a basement if financially possible. But I still doubt the measurements.

I have marked the building plot with a red arrow and it is located at the top left. Although the plan shows that the depth can be max 10.5m, the building line is directly on the street (there is no stepping back) and the municipality has indicated that you could/should definitely build 1m away from the building line (the whole thing was designed by an architect as part of a competition and he "didn’t really think through the building line properly," quote). So there would be 9.5m left, but we are thinking of using 5m for the garden and not just 4.5m.

Keep garden stuff compact.

With 225m², there probably won't be much garden stuff. It's actually outrageous that something like this is sold as a building plot. I would personally definitely build with a basement, as you can keep the house more compact above ground and maybe still have a few meters of garden left. But I also built with a basement on my plot; I would never do without a basement.