Floor plan design for a single-family house for 4 people on a 390 sqm plot

I was fully aware that your footprint is atypically square for a terraced house before I gave my advice. I speak from conceptual experience. When I started designing residential buildings, there was "no Internet at all yet" ;-)

What speaks against this straight staircase at 10x10? Can you explain that better? Here the distances in the hallway are given, and you don't stumble directly over a stair step when entering the house. Although a lot of space is lost on the upper floor due to the staircase, it does not result in any narrow rooms?

Put differently: From what dimensions is such a staircase suitable, or why does the house not look like a city villa? Many city villas do not have larger exterior dimensions after all?

In short: From which dimensions can a house appear like a town villa and a straight staircase can be used accordingly?

At what dimensions is such a staircase suitable, or why does the house not look like a city villa? Many city villas do not have larger exterior dimensions anyway?

At what dimensions can a house look like a city villa and a straight staircase can accordingly be used?

I see no connection or contradiction between the straight single-flight staircase and either the Anstattvilla or the city villa. This design has almost the typical Anstattvilla footprint. Regardless of that – because independent of it – I recommend not putting a single-flight straight staircase on the wish list for house widths under twelve meters.

Why exactly 12? Because the staircase is 1 meter wide and anything under 12 otherwise results in "right" and "left" tubular rooms? What, for example, is wrong with the proposed floor plan here with the straight staircase? Maybe you could explain that a bit more closely? It actually looks like the hallway is 2.50 meters wide, which is completely sufficient.

I don't think the floor plans are bad. I especially like the upper floor. But I also like hallways.