Assessment of Financing New Construction 425k € / Overall Financial Situation

Interesting. When were these houses built? You could ring the doorbell there and validate the architect's cost estimate. It would be nice if it even turns out that the architect's cost estimate is realistic and still up to date.

Regarding the table: Is there already an item for vacation? What about the purchase and repair of new cars, or do you lease everything completely?

2000€ net for the woman results in parental allowance of 1300€. For one year! Spread over two years, that's 650€. And even then, the two years might not be enough, since daycare spots are almost only taken in August, because only then are places freed by children starting school. If your situation is tense, parental leave can quickly become 2.5 years until the woman goes back to work. Does daycare cost anything for you?

It will definitely be a long dry spell with kids and a mortgage :(

You can optimize parental allowance if you get married and assign the better tax class to the woman now. I believe the Greens want to extend parental allowance.