Floor plan design single-family house 150 sqm - tips for improvement?

The hallway is not the problem with an open wooden staircase

I also find the whole thing not very inviting even if it is open, that's just my subjective opinion.

The kitchen details don't matter at this early stage anyway

That's not entirely true. Depending on how important the kitchen is to someone and whether they have a dream kitchen that absolutely has to fit in like that, then you should already consider how the room needs to be so that it fits.
Connections must also be planned for this as well as for the bathroom.

Which variant are you referring to in each case?

The connections for the bathroom need to be planned

I already wrote that. However, the position of the bathroom is sufficient.

not quite right.

Referred to the "counter", not the entire kitchen.

And yes, much is subjective. But open is not as bad as closed :-p

I prefer 4a. I find it appealing to plan the senior bedroom from the outset along with its entire suite downstairs. I like the floor plans only until I see the elevations: I find the brick cladding borderline appropriate, but the hipped roof especially with the recessed floor is an unsuitable combination. On the other hand: since last Saturday's Wilsberg, I know that Overbeck likes liver sausage with applesauce.

Which version are you each referring to?

I mainly looked at 4a and posted about it.

The staircase on the 4th floor is also positioned a little further away from the entrance, giving it a slightly more spacious feel.