Single-family house cube without roof with full floor

I would reconsider the kitchen. Not reducing the kitchen unit, but moving away from the show kitchen. The house is too small for the kitchen

Different staircase.
A straight staircase and the show kitchen are space eaters.

2 architects recommended the straight staircase to us because it provides more space upstairs.

Do you also want to build in Berlin?

No, it is a small village, directly on the border. 10 km from our workplace in Berlin.

2 architects recommended the straight staircase to us because it provides more space upstairs.

A straight staircase takes up the most space.

And the insulation, meaning the total wall thickness, must fit the floor area ratio.

2 architects recommended the straight staircase to us because it creates more space upstairs.

Space for what? For the staircase?
A straight staircase usually takes up a lot of space. But it always depends on the wishes. The shape of the staircase often results from the arrangement of the rooms – unless the builder makes it priority 1.

I’m missing a bit of information about what exactly you want. The house will be very noisy. The children sleep poorly if Mom and Dad are still clattering pots downstairs or watching a crime show. Do you want to live so openly?

The house is too small for you? Then build with a basement. Since the terrace will probably also have to be deducted from the floor area ratio, I would try to plan the basement in as well.

A straight staircase takes up less space. You have a large hallway/gallery upstairs. Your upstairs hallway is almost as big as the children's rooms. Different staircase, different location, and you would still have an office/guest/whatever room upstairs. Open-plan living is great. It still has disadvantages. A room where you can quietly make a phone call or just open the door, put stuff in a box, tidy up, doesn't hurt. I wouldn't plan the garage as a storage room. They are actually not allowed to be used for that.

We have a very open floor plan, but it’s just the two of us. And even then, sometimes the noise level gets on your nerves (and we’re both on the quieter side ) When I imagine that with children...

I do like the floor plan you drew, but for such a kitchen and the staircase, I think the ground floor would have to be significantly larger.