Semi-detached house, approx. 140m², 2 full floors

Can't you do without: side entrance,

Why?
What is the reasoning?
Could you please upload the plot including the parking spaces and the access path?

The thing is: the hallway is not nice at all. In addition, the staircase is not ideal for this house. The hallway here is even longer than if you were to enter the house from the short side; from the short side you would have a nice view from the hallway into the living area. Here you look at the office door, which is rather in the dark area of the house. The guest is directly in the line of fire when they want to go to the bathroom.
The kitchen feels uncomfortable due to the two openings. It appears more open than an open kitchen, which you would arrange to be homely. It gives the impression as if there is still hallway space and only a niche is furnished with a kitchen.
A different staircase or staircase location would also appear somewhat more positive upstairs.

My predecessors are of course right when they complain about the missing wall thickness. It is easier for a layperson to use thicker walls than necessary than the other way around – many things will no longer look so effortless when you revise them.

Only possible with a reduced step depth (approx. 25cm).

I doubt that, because you only calculated 14 risers. What is the intended floor height? That is, clear room height plus intermediate ceiling. The 285 cm from the examples is actually the minimum standard. That already results in at least 20.35 cm step height with 14 risers.

Regarding the attic conversion: Have the roof insulated directly and not just the floor of the roof, and also plan a proper staircase from the beginning, even if you don't want to start the conversion immediately. Otherwise, you'll just be annoyed in 5 years. The downstairs is also awkward. A kitchen in a two-line layout is an option? That way, you have a more open living room and place the cabinet in the living room against the red wall. Possibly rotate the dining table by 90 degrees. Is the study used regularly or could it possibly be moved to the basement – if there is also natural light there?

Hello,

Changes:
- Wall thicknesses adjusted to realistic values. All exterior walls to 40, interior walls to 20.
- Staircase half-turned with 16 steps, dimensions 240x240

The office is used almost daily. I do not want to go into the basement with it.

Entrance on the side for 2 reasons. A rear entrance would create a long (6-7m) corridor to the living room. With a corridor width of about 1.5m, I don't imagine that to be very nice. Inside, I want enough space to comfortably put on jackets and shoes. If you have any ideas on how the entrance area can be moved to the back, I am open to suggestions.

The attic conversion is being prepared. This means stairs up to the top, piping for a bathroom is being installed, and partial walls are being built. Insulation is also planned to be installed under the roof and not on the floor to the first floor.

Entrance on the side for 2 reasons. With a rear entrance, a long (6-7m) hallway would be created leading to the living room. With a hallway width of about 1.5m, I don't find that very appealing. Inside, I want to have space to comfortably put on jackets and shoes. If you have any ideas on how the entrance area can be moved to the back, I am open to suggestions.

So, as I already said: You now have a longer hallway than on the short side. My personal opinion: Remove the stairs, move them somewhere else, another staircase, whatever... but as it is, the kitchen is simply pushed into your large hallway. I think the whole room layout is not well thought out.

.. and without necessity to be able to enter the large open space only through the kitchen, and even in a zigzag - is a struggle