Please assist in thinking about the floor plan of a single-family house

With that size, quite a bit should be possible. However, the arrangement of the rooms is completely baffling to me. The kitchen should be closer to the terrace than a guest room, right? If this is the result of a longer consultation, I wonder if your wishes are so specific or if the planner is so unmotivated?
I would start over.

Thank you also for your feedback! This is not the result of a longer consultation. The thread can please be deleted by a moderator and we will get back with a new floor plan.

You don't have to delete it, something is developing and your requirements and wishes remain.

The staircase ruins everything. I would plan with a new staircase. Swap the children's room and bathroom. Do you really need a study and guest room? I would add additional soundproofing to the wall to the building services and storage room.

Now don't give up so quickly on this floor plan, which of course raises a few questions. I will try to comment more specifically:

1. Kitchen: I found it pleasant in our last house to look out onto the street from the kitchen when the children were still smaller and playing on the street/playground opposite. The path from the kitchen to the front door is anything but practical: long and leading through the living area.
2. Guest room: Guests get a very "prominent location." There are guests and situations for which this is gladly done.
3. Ground floor hallway and stairs: Surely the hallway is rather dark, but that can be quite well solved with lighting - the hallway is not a permanent living space. It is good that space for the wardrobe was considered - this sometimes goes wrong here. The staircase is a space miracle - one wonders how much space it takes. For a "design centerpiece," one can certainly do something like that. The central location has the advantage of giving the other rooms more exterior wall and thus a chance for light.
4. Upper floor hallway and stairs: You do not use the possible advantage of a lot of light in the rooms around the central staircase - none of the rooms are "flooded with light." As you already say, the circulation area is quite large. The way to the bathroom is very far for one of the children - the child will not mind though.
5. Storage - laundry room: I find the positioning above the front door great. Short distances for all laundry and bright. I really like this aspect.
6. Rooms on the upper floor: The size of the rooms is okay. Nevertheless, it is hard for me to imagine that the rooms will have the desired effect, as each room has a lower height or a sloping roof on one side. In addition, the arrangement results in too many niches, which makes the rooms somewhat harder to use. A niche is basically not a problem if you plan to use it. A niche that results from the adjoining rooms rarely fits well with the room. These challenges on the upper floor are a result of the staircase arrangement. (As previous writers have already noted)

My conclusion: The planned house is too small for the realization of a central staircase - both in terms of floor area and height.

What is most disturbing is not shown, namely the drainage of the bathroom upstairs. Imagine the drain next to the sofa, visible on 20 x 20 in front of the exterior wall. I wonder why the bathrooms are not stacked. Even with the annoying stair position, the upper left location on the plan would be better for the bathroom, and accordingly, room sizes could have been adjusted. In this respect, I will not go into missing doors or such small stuff, because the upper floor definitely needs to be changed for me.

I have been a silent reader for years

Let me put it this way: the floor plans do not reflect that.