Regarding the topic of wannabe Bauhaus in a §34 area from the 70s with exclusively pitched roofs so far, I can only say that we got approval without inquiry. So it is not impossible. Nothing ventured, nothing gained.
As you can see, I also live in a stylistically similar house. However, I also believe that you should first detach yourself from the exterior and get it functional inside. I consider the dining area very unfortunate, simply too narrow as a permanent passage to the kitchen. Garage as storage space is good and fine, but you cannot store anything sensitive to cold or moisture there. If you build without an attic, you have to put a bit more thought into storage planning. How old are the other two children?
With soon to be three children (although small ones), we have a technical room of 8 sqm, a utility room of 18 sqm, a pantry of 4 sqm, and a cloakroom as a sluice to the garage of about 8 sqm. Additionally, a double garage with a 3x6.4m extension for storing everything that does not necessarily have to go into the house. And without an attic (also because of the flat roof), that is far from too much storage space. In comparison, you only have a freezer room, which will not offer much more storage space besides the appliances. Even if it doesn’t look so nice, I would also separate the small study on the upper floor structurally. If the office then moves into a child's room, even better. At least you gain a small storage room.