Newly built single-family house, approx. 180 m², for 4 people, without basement, RLP, KfW 55

You can definitely hear the TV upstairs clearly when there’s no door in between, just as you can hear the kids’ music in the living room. For me, it’s simply more comfortable with kids and pets if you can still close a door.

Best regards
Sabine

So we have the choice between a long, possibly dark hallway with a door, but quiet, or a more open living area with the risk of it becoming noisy. Somehow difficult. In the current house, everything is "sealed off" and unfortunately we have no experience with open spaces so far.
Pets won’t be a problem since we certainly won’t get any

I also like the floor plan. Whether the kitchen size is sufficient really depends on your priorities. I certainly wouldn’t arrange it like in the plan.
You could take a look at the Weiss Musterhaus Ulm. It’s a variation and the "more open version" of the kitchen.
There they solved it structurally by leaving a wall panel standing. For example, a kitchen island could also be "docked" to it.

Is it a structural problem? Well, not a problem in the sense of unsolvable. Problem in the sense that the structural engineer might have to add more rebar or concrete, yes. Costs a little extra. Your builder must answer you how much.

Noise... well, opinions differ on that too. Sure, the more open, the more "noise" reaches upstairs. The Weiss Musterhaus Ulm even has a "void" included. Whether you need that is debatable.

Thanks!
We are not very picky about the kitchen and thought that a peninsula with a cooktop, a row of cabinets on the wall facing the office, and tall cabinets on the wall facing the hallway would do. Usually, only one person is in the kitchen and we are no star chefs either.

The wall panel is a good idea, it was also like that originally. The question is how open we really want it to be towards the hallway in the end regarding the noise issue.

No, just different.

Wall panel for example or a column. I would do it with a wall panel. You could also add a wall panel to the stairs and separate that from the kitchen.
My idea of the coatroom airlock is something I would still try.

How should I imagine the airlock? The door would currently not fit under the stairs in my opinion, meaning I’d have to move the stairs and/or the wall of the utility room towards the living room, right?

The wall panel is a good idea, it was also like that in the original. The only question is how open we actually want it to be towards the hallway in terms of noise issues.

Then just do it that way. Maybe as an idea for your noise concerns. I don't know what kind of staircase is planned, but if a closed staircase is planned, you could also use glass elements instead of a stair railing. That might not be top sound insulation class, but it might at least somewhat reduce the clatter in the kitchen. And it also looks stylish.

Then just do it that way. Maybe as an idea for your noise concerns. I don't know what kind of staircase is planned, but if a closed staircase is planned, you could also use glass elements instead of a stair railing. That might not be top sound insulation class, but it might reduce the clattering in the kitchen somewhat. And it also looks stylish.

So far, a concrete staircase with a masonry railing (handrail and steps in oak) is planned. Would you build the staircase "closed" – that is, with a wall? The glass panels could possibly also be realized later.

By open staircase I mean that you can see through between the steps, not whether there is a wall on the side.

So far, a concrete staircase with a masonry railing (handrail and treads in oak) is planned. Would you build the staircase "closed" – that is with a wall?
The glass panels might possibly still be realizable later.

You have a closed staircase (concrete staircase).

Yes, it is definitely possible afterwards, but then only the distance between the railing and the ceiling.
My idea was a staircase up to the ceiling. That looks lighter.

So we have the choice between a long, possibly dark hallway with a door, but quiet, or a more open living area with the risk of it becoming noisy. Somehow difficult.

....I don’t find that at all-. With the first sentence, you’ve already made your (correct) decision or do you really want such a hallway? I think that people often assume extreme situations. Of course, there will be moments when it would have been better to do one thing or the other, but the rest of the time—and that is the real life—you enjoy the actual decision. In this case, I would always advocate for an open solution. We, for example, lived on one floor with 2 kids plus a dog! and that was completely trouble-free. The children didn’t even close their doors at night but just left them ajar and slept perfectly. You don’t watch Terminator or a Danish western at full volume every evening… that only happens in your imagination. You even have an extra floor, which is why I wouldn’t see this as a real problem but rather as a perceived living comfort.

The hallway does not have to be dark, there are also doors with glazing.

Best regards
Sabine