Design for a single-family house with 160-180 sqm - suggestions for improvement?

Are there any indications besides the staircase issue and the 2sqm that result from it? Although a landing staircase wouldn't have a door to the basement either, so all the cold would come up

Not if you include the room in the thermal envelope. Do you want to leave it unheated and insulate the stairwell and install an appropriate door? Where do you drive onto the property?

Access would be planned from the left - pretty much exactly where the black solid line is on the plan. It should be the lowest point of the property. However, a basement within the shell costs significantly more, right? It would mainly be just a technical storage room and garage downstairs. Can the garage be left out of the shell and the rest included?

You can also build a wall around the staircase with a door, before you rack your brain about the cold.

You can also build a wall around the staircase with a door before you rack your brains about the cold.

With a landing staircase?

You can also build a wall around the stairs with a door before you rack your brains about the cold.

That was already advised anyway - we are going in circles...