Single-family house 175 sqm without basement, too big?

I would widen all the windows by at least 30%. Or have more windows, depending on taste. In any case, in my opinion, it would be too dark.

I spent some time working on the window planning. Attached are pictures with the window dimensions (width x height).

At least you were disciplined regarding the number of different dimensions. From that, I deduce the sill height of 98 cm for the standard-height windows. But could you enlighten me why you (also with the room dimensions, not just the windows) specify very special measurements – on the one hand deviating from the standard measure, but on the other not aiming for the usual round decimeters as laypeople would expect? – is that coincidence / astronomy / lottery numbers / Aunt Trude’s birthday (because: I see neither particularly “drinking game” nor prime numbers, but also nothing in the standard measure, everything “individual”)?

To what extent special room dimensions?

I have the window dimensions from the window catalog of the house manufacturer we will be building with. Or do you mean the combination of the windows? ops:

I have the window dimensions from the window catalog of the house manufacturer with whom we will be building.

Which one would that be, is the catalog available online? For solid houses, the octameter grid makes sense, and "prefabricated house" manufacturers usually have construction and planning grids, but I do not recognize either here. The window widths 109/138/175 also have no apparent pattern or "common denominator" (?)

The manufacturer is Schwabenhaus. I honestly removed all the interior walls from the house and created the floor plan myself. When it was finished, I first tried to reuse the originally planned windows, and otherwise freely chose windows from the catalog. As far as I know, the catalog is not available online and I do not want to release it...

I also very much welcome optimization ideas for the floor plan. It seems you would change quite a few things.

Manufacturer is Schwabenhaus. [...] Seems like you would change quite a bit there

Schwabenhaus is a "prefabricated house" manufacturer - that at least explains the dimensions outside the octameter system, but I still don’t find a planning grid (classically usually 62.5 cm) here. Not a big deal. No, I’m not really itching to change much: Your planning is already much more clearly structured than what I’m used to from this forum. So far, I haven’t noticed any major blunders.