Single-family house cube without roof with full floor

I’m sniffing out quite a spectacular resistance to advice here again.

Build however you want.
You have received enough suggestions to think about if you want. If not, just leave it. But I do find it relatively rude to snap at the people who engage with your draft like that. Please think about it.

That all sounds somehow uninformed to me, which is okay, that's why you're here.
If you want a chicken ladder, be my guest. Then just climb down the stairs with the laundry basket on your head. Good luck with that. And if you like that your teens' friends run past you up and down the stairs three times every evening by your cozy sofa - go ahead. We're just giving tips here.
However, I have the impression that you reject many things rather than seriously consider them.
For example: if the staircase is planned to be 1m wide, then about 3cm (in our case rather 5) cheeks are lost on each side, then railings on at least one side (better both), and depending on the shape, sometimes step widths have to be considered for turns. And then not much is left of the 1m-wide staircase.
With your kitchen layout including the dining table, you have a mega long corridor in which you are trapped. Then you run back and forth on the 1.09m all the time. I don't find that so bad – if you like it. It gets interesting when you draw in the chairs.
The view when you enter the hallway and approach the narrow but open entrance to the kitchen is also poor. You see the side of the kitchen unit. To me, a piece of wall is still missing there. The wall to the WC, on the other hand, is completely unused, but you can hardly get past the kitchen island... etc.
These are all just sketches – that's why I don't find it bad, and hopefully the architect will eliminate such things for you. So for my part, I'll wait for the professional design.

Which Gussek house is this?

Townhouse Gussek House Manhattan, ~144 sqm

Where do I say that? Are you building without money? 280k. I already said plus additional costs. If it works out with the Polish stair builders, the folding structure will be made of wood. If not, regular ones made of concrete.

It's stated right up there. That the financing is almost done. How do you know the construction will cost 280k€? You don't even have the floor plan finished yet. Is the cost estimate from the architect who thinks a straight staircase saves space :-p? Honestly, nobody here wants to harm you, but everyone just wants to make you aware that you haven't done your homework yet and that you should take one step at a time in the right order. So you can skip the snappy replies.

Just to be clear, I’m not building this house for my visitors. And if my family visits once a year, then it should be logical that this is not the top priority.

Nobody is saying that. Only your argument is in question. It is ill-considered. Now one could just keep quiet... let her build and realize later that it wasn’t fully thought through.

Well, I know from my relatives and acquaintances and I was once a teen myself – it was enough to retreat to your own room. I don’t see what should have changed if I had 220 sqm? The children would still only have one room. So I find this argument nonsensical. Each child has about 15 sqm.

Nobody is saying the children’s rooms are too small.

Where do I say that? Are you building without money? 280k.

He means that you should wait for the calculation from the house builder or architect before finalizing the financing because you don’t know how high it will be if not even a draft exists yet.

I don’t understand why the staircase should be 1 m wide. Why? To walk through there for a few seconds once? It will be narrower.

Because the risk of accidents increases the steeper or narrower the staircase is?!
You will walk it longer than a few seconds when your child wants to come along (holding your hand) or when laundry is carried down daily.
Zick, zick... I always wonder about the point of higher rooms.

City house Gussek Haus Manhattan, ~144 sqm

Which has absolutely nothing to do with the OP’s wishes.

Do your thing, but don’t whine here when time is taken for YOU.
We can only give hints.

That's exactly why I'm here—to exchange ideas and maybe even give tips someday. Snappy answers? Why? Not my intention. That was meant to be a rhetorical question. I don't understand right now; I address every question. I take to heart everything recommended here and also give a general opinion, as far as I have experience with it. And if I think that an interior design can and even should be mixed, it's precisely these contradictions that I like. Then that's just how it is! It's nice, after all. Besides, that's not the topic. This is my first time building, and I think my attitude toward certain things is rather normal, and people shouldn't twist my words (so for those who try). Resistant to advice? Of course, I went to the architect who told us it would cost 280k including incidental costs; we include furniture. Only one wall was moved, and that would not change the contract sum. Plus or minus a few thousand maybe. A Polish company quoted me €5000 for the folded staircase; I get quite a few private messages here. And maybe the craftsmen are cheaper or whatever. Naturally, a stair builder from here cannot compete. Not even the one from Berlin. This is a new development area where the architect has built about 200 single-family homes nearby (!). So why shouldn't the price be right? I researched every trade again, and except for a few items, I was more expensive. And I will, I hope, discuss the floor plan with the architect before Christmas. The staircase situation is really as some say, but it fits very well in our house, and if it were quarter-turned, we would have more space downstairs. That's clear. You can discuss that. In our case, it's more space-saving since we definitely wanted the kitchen to be lengthwise; otherwise, the hallways would have been too narrow. But surely, it's clear that in a standard floor plan from xy construction, the bottom right has many turns for 125 sqm.

To maybe make it clear again: I am really grateful for every opinion or discussion that might also encourage other readers or something like that.

I just wanted some opinions on the floor plan and tips. And if I get some advice on my curtains as well. Ok! I’ll take it! Why not? But then don't be offended if I don't share the same opinion and say that I'm snippy or something. That's not acceptable.