Floor plan single-family house 150 m² 448 m² 1.5 stories

If office, then the bedroom would have to go into the basement, thanks to underfloor heating theoretically no problem even in the basement. But the basement only has one light shaft per room. So hardly any light. -> That is our main problem with the floor plan.

So that means the basement is also included in the thermal envelope and becomes fully usable living space? That would be about 210 sqm of living area. Then the 430,000 EUR will be very tight. What else is supposed to be installed?

So the basement will also be included in the thermal envelope and will become fully usable living space?

Thermal envelope yes, but due to the lack of windows and the inability to build further upwards (limit first-floor height around 9m), the room height of 2.30 m is too low for living space according to the standard.

Then the 430,000 EUR will be tight. What else is supposed to be installed?

Central ventilation system with heat recovery, nothing special otherwise. 430K is the fixed price including price guarantee.

My question was more about how you just came up with Horst van Hümpel.

You really don't have to look for him. You can even see him if you don't want to build at all, he builds so many houses. And not every house is rubbish.
However, I would not do without an expert with him either!!!

...

My own floor plan "failed" here in the forum, ;-) so my opinion probably only has limited value, but I find your floor plan okay.

Are roof windows planned? If not, maybe you could inquire about prices to see if it is feasible. Then the rooms on the upper floor would be brighter. (In our previous house, we retrofitted roof windows in two rooms and the difference in comfort was enormous.) Maybe it is at least possible for the children's rooms, which should also be nice and bright on gloomy winter days.

Can something still be changed regarding the number or size of a light shaft? Bedroom in the basement (maybe you should rather call it basement instead of cellar) has advantages. Ultimately, it depends on what kind of people you are, but I would especially value the privacy and possibly the retreat room in the basement, especially with three children. In addition, the basement is also enlivened by this. Unlived-in rooms or floors, ypg once aptly called them "ghost rooms," I find unpleasant. If a room in the basement is regularly used, that radiates to the other rooms in the basement as well.

The no-go in my opinion consists in the loveless planning - ...

Could you please explain what you think the lovelessness consists of?

But (spontaneous visitors) guests should still be led to the sofa for a drink and then see the chaos in the kitchen...

I am a fan of closed kitchens and do not want to question your related decision. To relieve you a bit, I want to mention that with 3!!! children, one never has to apologize for any kind of mess, no matter where it is, nor will it bother anyone. That is the privilege of living with children. :)

You could still consider whether you want the open kitchen because it suits your wishes or has been fashionable for a few years.

Then the rooms on the upper floor become brighter.

I did not look at the windows: upstairs I would choose ones with a parapet, about 2 meters wide. A room gains more light through width than through vertical slits. And yes: opposite the doors, double casement windows would be quite good. The bathroom is quite well done, I would forgo the 140 cm shower and give the toilet more space. (The shower must be separated at these sizes.) You could cut off the cloakroom here, and unfortunately, a cozy kitchen for 5 people is quite negative. You probably get MORE kitchen if you swap the living room and kitchen. The living room can do without a door, if you want, the kitchen could be an L-shape, possibly a U with an island… be sure to draw in a realistic dining area. I give you the advice: deal with the floor plan yourself: copy it by hand on millimeter paper. Get a feeling for what a meter is, and what you can get out of it.

Aren't there skylights drawn in all the bedrooms on the upper floors? It looks like it to me.