Spacious single-family house planned over 200 sqm

Thank you very much for all the answers and inspirations so far. It is a floor plan created purely by us, based on a house seen in real life, which we want to take to the construction company. I have not yet had the cousin's floor plan in my hands. That we may currently have somewhat oversized (in the hallway on the ground floor) or that we might not be able to stick to our gut-set budget of 450k is therefore not so surprising.

I actually understood all the answers except for the following:

Does the development plan really not specify anything?
With 2 full floors and a 25 degree roof pitch, you have about 40 sqm with over 2 m height. Keep an eye on the area

How do you get to 40 sqm? In which room? The roof pitch only affects the height/form of the attic, right?

Oh yes, and what do you mean by SIMs house? I did play SIMs before as well, but what makes a floor plan a SIMs house?

Correct. With a roof pitch of only 25 degrees and your house dimensions, approximately 40 sqm with over 2 meters of standing height are created. About 30 sqm with more than 150 cm height. Attics can be converted into living space with daylight without expensive earthworks. A small apartment fits in there. What does your development plan say?

Oh yes, and what do you mean by SIMs house? I used to play SIMs as well, but what makes a floor plan a SIMs house?

A Sims house is planned meter by meter, sometimes 20cm is enough, the Sim planning turns that into a whole meter. It's not really planning.

If cost efficiency matters - and the reason for the high knee walls suggests that -

I have not yet encountered an increase in cost efficiency through high knee walls (?) - high knee walls usually go back to the delusion that one needs a feeling of spaciousness, that with the ass against the wall in every corner of the room full head height would be required.

I have not yet had the cousin’s floor plan in my hands.

Then just get it. We can imagine the deviations from your wishes there, but then you would have the template once "in functioning".

An increase in cost efficiency through high knee walls is something I have not yet encountered (?)

It was the reasoning behind it, not the fact.