Floor plan single-family house approx. 140m² - separable staircase

In my opinion, the staircase is arranged somewhat unfavorably.
The access from the corner or from the short side leads to relatively long corridors.

The toilet can be made separate. Each option has its pros and cons. In our case it is locked, then the bathroom is just closed off. Others suffice with a privacy screen and others again have a separate toilet. Everyone as they like it.
The separate toilet is probably a few hundred euros more expensive, due to more tiles plus an additional washbasin.

What I believe is the biggest problem in the discussion is the statement about the partition. And there I also see the problem:

Thema Treppenhaus:
Dies ist problemlos abtrennbar, indem man das Treppenauge (gemauert) verlängert und nach unten mit dem Kücheneck verbindet.

I don’t see it that way. Draw the wall into the floor plan and then try to close the door to go up the stairs. Alone it might still somehow work. With two people or with a shopping crate, definitely not anymore.

Die Küchenanschlüsse/Leitungen kommen ins Kinderzimmer Süd. Die 2 Kinderzimmer werden mit Durchbruch und mit einem Balkon im Westen das Wohnzimmer/Küche.

The only continuous (possibly also load-bearing) wall will be removed and then? Where does the kitchen go?

We also once briefly considered a separable ground floor, but quickly dismissed it again. I believe this only works sensibly with a certain house size. You have simply "wasted" too much space on the ground floor for that (setback entrance and long corridor) and the upper floor will never become a reasonable self-contained apartment.

The separate toilet is probably a few hundred euros more expensive due to more tiles + an additional washbasin.

There is also the additional door with at least 200€. In principle, I don't think a separate toilet is that bad. I had it in my parents' house. Especially with daughters, at least you can use the toilet if one of them is occupying the bathroom. However, in our case it was at a 90-degree angle to the bathroom door, so you could quickly dash across the hallway from the bathroom with or without a towel. Regarding the topic of separable living units, I see it like everyone else. If, then sensible. A small bedroom might theoretically be enough for you now, but in old age? And do you really want to give up the luxury of your bedroom + dressing room? That is quite a significant change! Also, how does the tenant (family or not) get to the basement?

What I just thought about: One could swap the pantry and bathroom, then you would have bedroom + pantry next to each other. The load-bearing walls would have to be swapped so that the wall between pantry and bathroom becomes load-bearing. If you move downstairs in old age, you can remove the wall between pantry and bedroom, which would result in a bedroom of about 5*3.4m. Additionally, you would have the entrance to the pantry as the entrance to the new, large bedroom and can brick up the other entrance (bedroom). This way you would have a completely separated stairwell, as the door to the bedroom no longer exists. Additionally, you still have the shorter path from the front door to the pantry and from the living room to the WC. Would that be an idea? We will still come to a common denominator.

Here are the pictures of how I could imagine it, the bedroom would then be approximately 17m².

So, at least it makes more sense for later.

By the way, we have now decided to leave everything as it was. My wife thought the kitchen corner was too important. Here, everything can be reached with one step. This would no longer be the case in the new design and it would be somewhat fragmented.

Nevertheless, we will remove the load-bearing wall between the bedroom and the bathroom, so that the ground floor can be designed like in the latest draft.

That means: both partition walls can be removed and a new wall can be built. Then the pantry will be eliminated and the bathroom and bedroom will become larger.

Thanks anyway for the suggestions, only in this way did the idea for the redesign for old age come up.