Floor plan and elevations for a single-family house of approximately 160 m² on a hillside location

On the subject of windows: Thank you very much for the suggestions. The design with the larger windows appears more harmonious to us laypersons. We will definitely take this suggestion into account.

On the subject of the basement: We will choose a somewhat lower quality of equipment in the basement than in the rest of the house. Cheaper floor coverings, probably also somewhat fewer electrical outlets, etc. So we hope that the basement level will then be less expensive than the upper floors. This is probably also a topic that we will discuss with the architect.

Calculation 1: €700,000 + 20% = €840,000 (architect often underestimates by about 20%)
Calculation 2: 250 sqm x €3,000 = €750,000 plus ancillary building costs €50,000 plus double garage €35,000 = €835,000
These are just calculations… ;)

However, the slope is not really a reason for a basement. It is leveled by the filling.

Regarding the floor plan: it's a pity that you cannot enter the garden from the living area at all, only through the rather small doors on the terrace.
And the kitchen is definitely too small: there is no space at all for tall cabinets.
Child bathroom drainage should be avoided through the dining area. Otherwise solid, if you disregard the calculation.

Thank you for the notes about the small doors. This fits the topic of optimizing the windows, which we also want to look at again. Indeed, it would probably be nicer to have a somewhat wider door (possibly a sliding door) leading to the garden.
Whether the kitchen is actually too small, I do not know. Friends of ours have a kitchen of a similar size; we will take a look and discuss it with them.

But that would be savings of maybe 4000 euros. Even with cheap doors and simple plaster, you end up at around 2200-2500 €/sqm. Depending on the region. Even in rural Lower Saxony, standard fittings are now calculated at 3000 €/sqm. And you are planning three full bathrooms and a fireplace and a lounge area in addition to the living room. Larger windows also bring higher costs. I would already mentally prepare for 50-80 sqm less.

I find the drainage of the children's pool exciting.

I have the impression that many architects still plan as if there were generous subsidies and low interest rates, so that the client can easily extend their budget.

In addition to the kitchen being too small, I also find the master bedroom very poorly designed, as the head of the bed is at the entrance, and the wardrobe layout is bad. And then the southern exposure. For that reason, child 3 has moved to the north. And with so many people, I would consider relocating the laundry to the upper floor.

Utility room/pantry .. almost 7 sqm, but in terms of furnishings, only one row of 2.9 m is possible. The wardrobe area protrudes in depth into the living room entrance area.

The garage access from the garden limits the terrace depth in the sheltered niche.

Overall, I still cannot quite picture the overall layout of the property. There will definitely be quite a lot of light wells in the south/east.