Floor plan for a single-family house without a basement / 4 persons

Attached are the cross-section and floor plan from the general contractor (with external dimensions 12.0 x 9.80 m).

Okay, if that was the basis, then you have already simplified it quite decently for a layperson. Am I correct in assuming that a design of this lackluster quality is only supposed to be an illustrated cost estimate and came about based on an absolutely non-binding preliminary discussion? (To me, it looks like the slightly snappy answer to the question, "Do you build houses with a 37° gable roof for people with two children and two cars?").

By the way, I don't understand a lot of things: 78.08 sqm attic is 85.32% of 91.51 sqm on the ground floor - that would mathematically be a second full storey. In the cross-section, the ridge height is nominally already slightly exceeded - so what is the reference height?; then you talk about 80 cm that the house should be higher and which I cannot find in the cross-section as well as which raises the question for me how you want to save the basement with that: that would be both an almost ideal plinth height for a basement without much light well excavation, and a basement abandonment according to my formula 40% basement costs. So my impression cannot be that a lack of maturity is happening at the detail level. I rather see the homework still lying far before the comma.

Basically, it doesn't look bad, but the assigned proportions seem unfinished to me. The open space of 47 sqm is not exactly huge but sufficient. In contrast, I see overly generous children's rooms, a difficult-to-furnish dressing room where you can't really dress. I had already asked once, unfortunately without an answer, whether all furniture in the house, including the respective intermediate walls/passages, are provided with actual measurements, as I see some tight spots there. The lower hallway has 18!! sqm, the guest room almost 16 sqm, which will probably be a home office. The technology could be sufficient, there is no utility room, and the usability of the narrow storage room (dimensions?) is not clear to me. The absence of a second shower in a family of four, given this need, would be considered a blatant design flaw in the year 2020; I am absolutely sure that this will be regretted in a few years, especially by the children, especially since it would be possible to at least prepare this; not to mention a possible resale value. The shower on the upper floor blocks the room like a block; I would look for another solution there. All in all, I stick to the fact that the proportions are not right; often you want to give children particularly large rooms, which does not necessarily affect their well-being and is expensive or means space is missing elsewhere. The hint from about a basement seems very sensible to me, although I am not a basement type. But that could make many things more appropriate. As I said, actual measurements, especially of furniture, would be important; I currently see the open space as very tight for the dining table/living area.

- The problem with the cabinets under the low KS unfortunately cannot be solved differently due to regulations.

that's not a problem, you just have to keep that in mind when planning.

the "storage room ground floor" is, for example, intended for two bicycles/sleds or similar.

now I feel like I'm being mocked. You want to push bicycles through half the house to park them? Tzzz*

The hint from @11ant about a basement seems extremely reasonable to me, although I am not a basement type.

I am also not a basement type in the sense of "pro basement," but rather "against paying no less for no basement than for a shared basement."

I will also give a few hints, overall I think it is already much better. You seem to be a bike fan? If the bikes are supposed to stand there, then put a door in the niche. But you are also building a garage. Wouldn't it be better to have space there for bikes and tools? I find the children's rooms big but I think good. I think that kids nowadays will live at home longer... The hobby room is also often used for storage, have you ever considered moving the window so that a large cupboard can still fit? Is a room planned under the stairs? Kitchen, you want it open. I will give the hint again that a closed kitchen offers more storage space and you could then also place the table crosswise against the new wall.