"Depression is followed by mania" would, in my opinion, describe the further course well.
Here is my update:
Short summary: did everything right and totally happy and joyful now! Since the end of 2023, we have been living in our new home, had a second child just before moving in (perfect timing), and manage all expenses easily despite my wife's full parental leave with about 350 euros in parental allowance.
Income has increased significantly since signing, last year I was on parental leave for 2 months, and we still went on several vacations.
So all in all, did everything right in retrospect and the lesson paid to the notary was worth it.
Best regards