Floor plan design single-family house 150 sqm city villa

No specifications regarding building style and roof shape and a relatively large plot.....

OH MAAAAAN!

You can really make something super innovative out of that!
Why always this super boring urban villa hip/hipped/mono-pitched roof boring house nonsense that literally everyone has now and where one house looks like the other?

Why a square floor plan when the plot is crying out for a rectangular one? (which would probably be far better for your requirements?). Or two interlocking rectangles/squares.

Floor area ratio/plot ratio also offer a lot of possibilities, I would look for a committed architect and create a dream house. Hardly anyone has such a situation. Usually, the building shape is very restrictively specified.

I really get teary-eyed when I see that someone has such a cool starting point and then wastes the chance with a run-of-the-mill house.

Give yourselves more ground floor area downstairs, then the kitchen will be bigger and possibly the entire living area better usable.
Upstairs you can put a smaller upper floor on top if you don't want to go over a certain sqm number and gift yourself a nice roof terrace (or green the roof)
I would probably build something very modern, cubic here, which primarily orients itself on the needs regarding room layout (and there are so many possibilities!), the facade design is oriented to the interior requirements (and not the other way around, as is often the case with urban villas, because the facade has to fit here).

*sniff*
I admit, I am jealous of the possibilities you have there.
Please, please at least use them somewhat!!!

(so in plain English: design in the bin, back to start, allow something innovative)

Otherwise: The purpose of the stair layout is not clear to me either. No cloakroom, that does not work at all with 4 people (just think about it, you all come home together, the first one takes off shoes and coat, and where should the others even have space just to stand? I don't even want to talk about everyone changing clothes at the same time...)
The kitchen would be too small for me too (but I am a confessed kitchen fetishist) and I always wonder why you need a counter when the dining table is just 1.5m away. I would rather have more cooking island for use (and possibly an overhang of the worktop into the living area and normal chairs for it that disappear under the worktop when no one is sitting).

But, as I said: I find the whole floor plan particularly unfavorable on the ground floor. Since you have the possibility to design a floor plan according to your requirements, I would distance myself from the very restricting concept of the urban villa and put something individual there.
However, if you are attached to the concept of the urban villa... well, then just square with difficulty and compromise on the interior layout. It wouldn't be mine...

In my opinion, this plot does not call for a city villa, but for a nice, flat Danish bungalow...[ ]

It’s not really necessary to fully exploit the possible plot boundaries, but at least the desired area here would also fit on one level. And whatever plot potential is still "left over" is enough for another dwelling unit for a tenant who’s not just a bachelor, comfortably with a separate "front door".

I already see potential for a clear longitudinal axis in the existing design, although I would already lay out the main house rectangularly (approximately > 1.2 : 1). I don’t think "city villa" is bad; what Hanse built earlier often appealed to me. I just get a bit of goosebumps when I see the equation of everything that is "flat roof white matte" with "Bauhaus".

Yes, a cube obviously has the smallest surface area (aside from the sphere) for the largest volume. That is an energetic advantage and, of course, also material-wise, I think. However, it would not be a decisive criterion for me.

Also Einliegerwohnung käme mir nicht ins Haus...