Floor plan design single-family house with around 150 m²

I don't quite understand what this should bring for the hallway?

The hallway doesn't care...

Opposite the stairs there is currently only about 1m of space, so the interior wall would have to be moved very far south, right?

Yes, that doesn't matter. Floor plan optimizations are done by moving interior walls.

And if the chimney is moved to the left, it will eventually be in the hallway on the upper floor!?

That's the idea! The advantage is that the room downstairs on the bottom right has more usable space. It doesn't affect the hallway.

Then naturally a child's room would be in the north, but maybe that's not so bad.

The child's room would not be in the north, but has the same window orientation as the other child's room in the west. The partition wall between the rooms should be optimized for 2 built-in closets.

Shouldn't the windows be aligned above each other on the ground floor/upper floor?

No, where does it say that?

Maybe the windows don't need to have the same distance from the exterior walls...

No, of course not.

Please take a look at your construction service description and the two threads

Please draw your existing or desired furnishings.

I have done that. Here are the floor plans.

Yes, that doesn’t matter. Floor plan optimizations are carried out by shifting the interior walls.

If I shift the interior walls to the south, the chimney is moved so that it goes exactly through the ridge of the roof. At the moment, it just passes by it. If the chimney is to be in the hallway (opposite the stairs), then I have to shift the interior wall about 40 cm to the south, which would make the living room very narrow from that point on (just over 4 m). In addition, there is the fireplace with a depth of ~80-90 cm, which would make the living room even narrower, down to just 3 m. As it is now, the living room would still have a depth of 3.5 m from the end of the fireplace.

That’s the idea! The advantage is that there is more space for furniture in the room at the bottom right. It doesn’t affect the hallway.

As the stairs are positioned now, I would then walk directly towards the chimney on the upper floor. It doesn’t bother me that the chimney is in the room. It doesn’t take up much space. If it’s to be in the hallway, something has to be thought of for the upper floor, maybe putting the stairs next to the bathroom instead of the bedroom or something like that.

The children’s room wouldn’t be in the north, but would have the same window orientation as the other children’s room in the west. The partition wall between the rooms would be optimized for 2 built-in wardrobes.

Well, it would then be in the northwest. It’s always somewhat cooler than a south side.
What do you mean by optimize?

You don't understand me [emoji2] Just because walls are moved doesn't mean the chimney is moved... etc.

Kniestockhöhe shall be either 1.25m or 1.375m,

The floor plan already has a knee wall height of 1m, and the drawn roof windows have their bottom edges at about 1.5m (in the bathroom even about 1.9m) – practically, these are already more skylights than windows that could still offer a view. The fuss about the chimney for the cozy fireplace seems almost funny to me in contrast to the fact that no such provision seems to be made for heating. With today's energy standards, a fireplace can only produce an excessive amount of heating power anyway, at least in a fairly small house. In my opinion, it also does not fit the budget dimension. I stick to my point: dare to sketch your own floor plan drafts instead of fiddling with a sample design that actually has nothing essential in common with your desired profile. The staircase can still be rotated, but even the wardrobe remains unfinished on the wish list without any other Our-house detail lurking somewhere else.