Floor plan single-family house approx. 160m², main entrance in the basement, north slope 1700m²

Where do your supply lines come from? Probably from the street? Then you can't have the utility room in the south, if the unheated basement room is supposed to be your utility room. I would immediately "dispose of" the general contractor for this mistake.

Then you cannot have the utility room in the south if the unheated basement is supposed to be your utility room.

Why not? They come from the east side, over the outer wall. Or do I not know better?

I wouldn’t want that plot even as a gift, and it doesn’t fit your budget. Even with very expensive modeling and slope stabilization, the plot is not easy to design or attractive. If I were planning for 3-4 children, I would miss direct access to and view of the garden. Living there would feel like living in an apartment. And before you keep dreaming about it, I would recommend seeing a civil engineer to be able to estimate the costs of terrain shaping.

I cannot agree with that. Such plots are very attractive. In our case, the terrain beyond our plot does not rise significantly anymore, which apparently is the case here as well. In a similar situation, we have sun on the terrace from early morning until late afternoon without significant shading from the buildings behind us. We naturally had to incorporate several retaining walls into the terrain. But as a result, our garden plants are now spread over several levels. This creates a very nice view from the terrace into the greenery. It is true that such plots are expensive to develop, and because of the retention basin, I would consider potential flood risks. An architect is definitely useful here. We didn’t have one at the time, and in the end, I had to completely change and adapt the general contractor’s plan myself. It wasn’t cheap, but at least we are satisfied with the result.

And being able to see the garden from the first floor wouldn't be enough for me - I would miss the direct garden access. We once rented a house where we always had to go through the basement to get to the garden. I would never voluntarily build that. Except with a large terrace on stilts and stairs to the garden. But that costs several thousand euros extra.

When I see his new terrain profile, he will have direct garden access from the ground floor living room. However, the terrain will slope down on the west side of the house. I'm not so sure if that's sensible. Depending on the incline, he'll need a long and expensive staircase there. And the slope towards the south boundary is not feasible like that; at least one terracing is missing.

Our neighbors paid 65k for the entire garden including the fence, with a few L-shaped stones 1m high, slope hardly more than 1m over 35m of land. With your 60k for earthworks, slope stabilization, drainage, you won’t make it, that should be a better down payment.

What happens during heavy rain? The slope behind the house will easily have 500m², all in all. With 50l in a short time, 25m³ of water rush down towards the valley or the house. You should actually build multiple terraces there, with L-shaped stones. An L-shaped stone 1.5m high costs 250 EUR per meter. Without foundation, without gravel, without drainage, without the excavator, without the landscaping gardener...

And you have to maintain all of that as well. 1,700m²...

I’d leave it, look for a flat, smaller plot. You get more out of that.

Because it fits right now, a current thread in parallel https://www.hausbau-forum.de/threads/wild-abfliessendes-wasser-was-ist-korrekt.47843/#post-667163