Judging by the overviews and the slope, the office door probably should not open outwards because there is a slope there? The staircase is not long enough! A bathroom without a window in a single-family house, where there are other options?
Otherwise, I cannot understand why they are planning anything other than 90 degrees here. Also, almost every room on the ground floor has unusable space: the children's room is almost not furnishable. Since you have ways to go outside on both the ground floor and basement, I find the idea of 2 separate living units for later okay. However, I would still initially zone for the family in such a way that the garden accesses are also utilized. For example, I would place either the parents or the child in the basement with garden access. And: a house does not need a long corridor, that is poor planning.
Regarding KfW 40, layman's opinion: every corner makes the house vulnerable, so a house that should consume less energy must be compact and have window orientation facing south. I do not know where the limit is that makes it harder to achieve KfW or Passive House standards or anything, but you cannot expect to just make the insulation thicker. What insulation thickness is used now? 16, 18 cm – the insulation performance will not improve indefinitely, and besides, it is insane to spend tens of thousands of euros on a house just so it meets some value only because there is a corner in the house. This is simply poor planning. When the specifications for the KfW 40 house are given, you have to adhere to the framework conditions, otherwise money will be wasted unnecessarily. I think achieving this will be difficult anyway if the house is adapted to the sloping plot: many windows facing north can already be a deal-breaker. I also do not see in your argumentation that you have a passion for KfW 40; you probably just want to build it because Ytong advertises good insulation properties as well as the subsidy (which, however, is spent on the additional costs).
