Is our new building realistically financeable?

The reactions were, however, in response to the post reminding that especially for older parents, retirement could be postponed because the life/studies of the children would need to be financed - regarding the consideration of loan duration. It is clear that there is a lot of gray area between black and white. But postponing retirement for the sake of the children is quite extreme.

Supporting means something different than financing. At least in my perception. But you only read what you want to read. Not directed at you now.... Just like the nonsense about a money shower, inheritance, etc. The idea that you work everything out yourself, save, and pay off apparently does not occur. For whatever reason...

I mostly agree here with

My parents didn’t have much either, they saved up a fund of €7,000 for me until I was 18, and that was it. For my high school diploma, I then received the fund and was allowed to choose whether I wanted to have it all at once for enrollment, or spread it out over the 60 months of standard study time. I chose the latter and thus received €120 every month for the 5 years of my Bachelor/Master studies. On top of that, €200 child allowance. That was it from my parents. There simply wasn’t more. My grandma added €50 starting from what I believe was the 5th semester. Otherwise, just €350 BAföG. So altogether I had €670–720 per month, from which I had to pay for my room in the student dormitory in Hamburg, the semester fee every 6 months, insurance, phone, clothes, groceries, etc. Since I studied one year longer than the standard study period, I worked as a working student during my Master’s because I no longer had the €120 from my parents. It worked!
And that’s how I think it should be, and that’s how we’ll do it with our son as well. I learned in a meaningful way what it means to have and spend money.
Since I noticed from the 3rd semester that I had more desires than I could afford (going out to eat, visiting my girlfriend in Lübeck more often, clothes, waterskiing once in a while, a new bike...), I looked for student assistant jobs. Or to be able to go to the Alps in summer, I washed dishes and worked behind the counter at a bakery 15 hours a week. It never occurred to me to mooch off my parents here.

The good thing for me was that I learned the value of money. After my studies (STEM), I suddenly had four times the income and, of course, besides paying off my student loans, I treated myself a lot. But I think that’s how it should be—building your own life for yourself, and not having mom and dad do it for you.

[...]not yet thought about retirement.
[...]pay an amount X every month for retirement provision

Find the mistake ;)

Not directed at you now....
Just like the babble about money rain, inheritance, etc. One apparently doesn't come up with the idea that you have to work, save, and pay off everything yourself. For whatever reason...

That was what I wrote. "Warm money rain" might have been somewhat inappropriately phrased. By that I also mean bonus payments, etc.
Or do you really pay off your mortgage completely from your monthly income in less than 15 years(?)?

here I disagree. This whole "obligated" thing. Yes, you have to provide maintenance. Here I would tell my children to keep living in the house, claim the child benefit, and then figure out how to do a side job.

"Stay living here" will work in a big city. For me, the next route to Ulm would have been, to the university certainly an hour (if the DB is willing). And honestly, the university in Konstanz was definitely more familiar than the one in Ulm. I also find it quite interesting how the keyword independence is thrown around here and then the children would be kept at home until 25. Or even longer. And partly the fear of helicopter parents turns into claiming children don’t need any support at all. Well, that certainly isn’t good. Our little one will in any case get sensible support, but she has to earn luxury herself. And as soon as she’s 3, she can also get used to the idea of taking the kindergarten bus. Finances are actually the smaller part of independence, and dad isn’t motivated to play taxi when it’s unnecessary ;)

Find the mistake ;) I had written that. "Warm money rain" might have been a bit awkwardly phrased. By that I also mean bonus payments, etc. Or do you really pay off your mortgage completely within less than 15 years(?) from your monthly income?

Of course, what else? We never adjusted our standard of living to the current income, so with 2 children we have more left at the end of the month than others with the same salary. The only thing that came unexpectedly was the Baukindergeld.

o_O We are - for various reasons - definitely "grey"... we like to support as much as necessary but only as much as we can. It was done the same way with us and we both found the middle ground between (1) worrying only about money and being independent (but self-centered) and (2) being lazy, money-consuming children. We will (ideally and depending on finances) orient ourselves towards our child according to their attitude and situation. Now back to the original topic - after our first serious "visit/conversation" we got a feeling, but regarding the price we are still in the 600k range (no offer, no floor plan yet, just based on our general idea). At the next appointment we will hopefully get a concrete answer on the topic of basement - necessary or not (because of the "slight slope") and then can continue with the floor plan planning. But we tend more towards "yes, we dare it" with the focus increasingly on reducing costs. How we manage that is still unclear, for that we have to plan various floor plans and at least get and compare a couple of concrete offers.