Dear community and everyone following this discussion: Thank you very much for the valuable tips and contributions, they were all instructive and informative.
In summary, our architect has now been dismissed, but I think there were already valid points that we simply would not have recognized without a "virtual sparring." We copied a lot from the designs created here ourselves and believe that with them we will reach our goal. Why do we still think the architect is not the right one? Honestly: The designs, among others from Yvonne or Würfel*, were so much closer to our wishes and so well-rounded in the overall concept that we asked ourselves: If a community can put this together, it must necessarily be a minimum requirement that an architect can do at least as well. If he cannot, he has to go. There were so many bugs in it, walls where none should be, recesses without reason... also the vestibule: With the old floor plan and the wall at the staircase, he would have fulfilled our wish for "privacy" in the living room without a second door (which obviously has a problem with >1 person in the room...), not to mention the somewhat more acceptable floor plan after we came up with the template. For the price, that is simply too little for us.
In this context, we also reconsider the question: architect to design, general contractor to execute? Or just general contractor? Well, some say that with the general contractor you pay the surcharge for the architect 1:1, but well... We will now take a step back and not force anything. We have now rented an "interim apartment" for two years and will take things a bit easier.