The maximum height of the knee wall, everyone says something different.

Depends on the builder... the cheaper ones probably not. And changing an existing floor plan costs quite a bit of money. Are you fixed on prefabricated houses or would a [Massivbauer] in the form of a [Generalunternehmer] also be acceptable?

A [Massivbauer] in the form of a [Generalunternehmer] would of course also be okay, we are quite open about that! What is special about the term "[Generalunternehmer]"?

What would be your concerns regarding the park and the trees?

Not the park, but the parking areas. The access would be on the northern border, and between the parking areas and the northern tree you have to servo-steered squeeze yourself through with a bad view, swinging widely.

Accordingly, one could realize a solid knee wall, possibly 1.20 or more? What do you think?

That may well be possible; I am still missing your specific terrain heights for calculations. A good knee wall has a clear height of one twenty plus or minus twenty.

What is special about the term "general contractor"?

A prefabricated house provider is one too, just not doing masonry. A general contractor is a "construction contractor plus," who offers you "turnkey" instead of just the shell. But I would always plan and tender with an architect, without excluding a GC, but not go directly to the GC without an architect.

It is important, in my opinion, to have an architect who is well connected regionally and who has already worked with the GU if he recommends one. Because with a GU there is always the risk that you buy the nasty fleas along with the cat in the bag. Regardless of whether the cat itself is mangy or not.

Because with a general contractor there is always the risk that you buy the nasty fleas along with the cat in the bag. Regardless of whether she herself is mangy or not.

You have me completely confused ...

In my opinion, what is important is an architect who is well connected regionally and who has already worked with the general contractor if he recommends one.

The architect should not "recommend" a general contractor, but rather carry out a tender, from which I only advise not to exclude general contractors.

Yes, but when it comes to the selection and he recommends a bidding general contractor, then in my opinion this recommendation should not be based on the fact that he is the cheapest or that the architect considers phases 7-9 to be "simpler," but rather that he also knows this for sure based on experience.