Questions zoning plan: distance carport-street, knee wall prohibition

What was the question again? Just call the building authority during business hours and ask your questions. They probably have to look up the plans first anyway and will call you back a day or two later. Then you'll know by the weekend.

our current house is from 1992 and absolutely does not fit the plan, although it is fully within the scope of the mentioned development plan.

I can't quite follow you: do you already live on the street where you want to build?

The legal interplay between the very old houses, the younger and unsuitable ones, and the new houses to be built is not quite clear to me yet.

If a valid development plan exists, it applies to new buildings within its scope as well as to changes to existing buildings there; it does not affect existing buildings without changes. If a development plan has been contested and repealed, it no longer applies (and is replaced by §34). For integration into the existing surroundings, buildings from before the plan and from the time during the plan’s validity count equally.

I can't quite follow you: do you already live on the street where you want to build?

Almost, one parallel street away. The plots border each other with their gardens.

Almost, one street parallel further. The properties border each other with their gardens.

Then you also don’t have far to go to the building authority or to take pictures (sometimes one is quite amazed which buildings are legally compliant with the plans, while every viewer would swear they couldn’t be).