Floor plan 1.5 stories gable roof without basement - Criticism / Suggestions?

yes, I also find it rather strange with the children who are supposed to move in. As an adult child, I would never come up with the idea, my freedom above all.

I always find it amusing how many here plan for at least one of the children to stay in the house. :)

It is not uncommon in rural areas. Rental apartments are scarce and one child will eventually get the house anyway.

GU as well as prefabricated house providers probably exclude themselves from the planned personal contribution, right?

GU does not, ours was happy about everything that was taken out ;)

It is not uncommon in rural areas. Rental apartments are scarce and the house will have a child anyway.

I live in a rural area. Most of my friends come from rural areas, NONE of us lived with our parents as adults. Considering that here it feels like every second single-family house is planned with an apartment for the children, this is rather a rare case that I would not plan for.

There was a 62.5cm "recess" for the living wall (...) to be found there, the side of which I later repurposed into the aforementioned slope.

Where "there"? – I thought the design was DIY?

General contractors as well as prefabricated house providers are probably ruled out for the planned own contribution, right?

Due to the wealth of complex connection details, I especially see ruling out contributing own work before the completion of performance phase 5 as well as the urgent necessity to have the planner also perform the construction management.

Not general contractors, ours was happy about everything that was removed

That often applies to mailbox general contractors – at least in times of rough seas regarding purchase prices.

And especially if the price was previously contractually fixed based on a turnkey scope, but the credits due to underperformance were not...
Thus, the general contractor/-subcontractor then secures their margin and generously carves out one warranty risk after another, fully aware that, strangely, the total house price does not come out when summing all trades.
Scheduling risk as well, by the way, because even if you had a construction period guarantee, they naturally only grant a minimal completion time for every removed trade, without buffer for scheduling and delivery times, and then extend the guaranteed construction period by the delta that inevitably must arise.