Planning single-family house with approx. 200 m² - Opinions wanted

What speaks against it?

That air, unlike water, is a poor heat carrier. As long as you are not building towards a passive house, you have to heat too much and that then costs a lot of electricity and money. Imagine heating with an air conditioner. That’s roughly how it works.

That air, unlike water, is a poor heat carrier. As long as you don't build towards a passive house, you have to heat a lot and that then costs a lot of electricity and money. Imagine heating with an air conditioner. That's roughly how it works.

Well, as far as I am informed, the system leads the once warmed air (yes, it must initially be heated) via a heat exchanger back alongside the fresh air from outside to keep the heating effort low.

I am not allowed to link anything here, but just google "Proxon ventilation system expensive business". It's a bit older, but I don't think anything has changed since then.

I will do it, thank you. Underfloor heating costs about €4,000 more with the system we have chosen, so it’s worth considering.

On the south side, there is a canopy running around the house that extends far enough so that the sun does not shine so far into the living area in summer,

... who plans something like that in Germany?
Such considerations make sense in South Africa and Southern Europe, but not here, even though we have had a few more sunny days in recent years.

We were exactly because of that with 2 kitchen planners, both said it is sufficient.

I wouldn’t have gotten my high school diploma with "sufficient." What else is the planner supposed to say to you? Oh dear, that’s a bit small? They always present everything more positively, that’s the basics of a salesperson.

I also like the layout: nice wardrobe closet, small hallway with necessary rooms on the ground floor... I like it when the dining table is the center and you place it in the middle of the house... I would have started the hallway under the stairs, that is, after the vestibule. Nowadays, immediate handwashing at home is a must, and you don’t want to carry beverage crates or trash through the whole house either.
In my opinion, the toilet is too far from the bed. I’m not a fan of these continuous hallways.
Many children’s rooms could be confusing if none arrive. If they do arrive and get a bit older, no one has peace or a retreat: parents sit in front of the TV on a display stage, and all residents and friends cross paths upstairs as well. With 200 sqm and wishes for children, a separate wing makes sense and has its purpose.

.. the kitchen planners primarily want to sell you something - no one here wants that.

Do some storage planning and see what will be standing around on your countertop. The kitchen also seems very spartanly planned for a household of 5; but if you mostly just put frozen pizza in the oven, then it should be fine.