Affordable house construction? Seeking expert help

You have good conditions for a relaxed house construction with solid financing. The only thing that causes stress is the 190sqm. If you leave out 40sqm here, you have enough buffer without having to go without luxury for years apart from the oversized bathroom and the living hall, and in the end maybe also a relaxed life. You do have an architect on hand, and for four people, he will be able to plan a 150sqm house according to your wishes.
Those would be my 2 cents on your question.

Oh and, yes, children cost money too, but out of the 24 hairdresser visits per year, 20 are dropped. That saves quite a bit.

You have good conditions for a relaxed house build with solid financing. The only thing causing stress is the 190 sqm. If you leave out 40 sqm here, you have enough buffer without having to give up luxury for years except for the oversized bathroom and the living hall, and in the end maybe have a relaxed life. You already have an architect on hand and for four people he will be able to plan a 150 sqm house according to your wishes. That would be my two cents on your question.

Oh, and yes, kids cost money, but out of the 24 hairdresser visits per year, 20 are canceled. That saves quite a bit.

I completely agree. Perhaps better 150 sqm, but already plan the double garage in case there is extra money at some point?

Thank you very much for the answers. Since we want to build without a basement (I don't see the reason), we need a technical room (12 sqm) and additionally an office (10 sqm) because we can both partially work from home. If you subtract that, it would be "only" 168 sqm, which is almost small for village conditions. But I also admit that we want to build some luxury (e.g. a small children's bathroom).

Regarding the garage, I am leaning towards a carport + storage room. Since I also don't see the costs there and there are quite nice ones.

But you don't have the money for luxury, that would have been possible 5 years ago.. consider parental leave, the daycare fees, etc.

400k with an income that is decreasing (children) forget it. It would be too risky for me. Stupid question fixed costs: 2 * 50€ hairstyle ???? What is that

Read again. You spend €100 a month on hair but only €250 on retirement savings??? Respect