Building a single-family house with a basement - Is the financing calculation too risky?

Unfortunately, I don't understand the first sentences, I just wanted tips like experiences, etc. My father-in-law was with the construction company; he was a civil engineer until a year ago and has also built houses himself. That's why we are on the safe side that the offer won't become too much more expensive, except that the issue of incidental construction costs with the earthworks can indeed be somewhat higher. See above, it seems that there are quite different opinions on whether we want too much or not. Indeed, it is so that we do not want to restrict ourselves too much for the house and it should be paid off in a maximum of 20 years.

I believe Milo3 meant that you should not let yourselves be unsettled by your framework conditions when it comes to the feasibility of the project. But there are a few risks and uncertainties that you should probe and also check where there are potential savings. I mean, in the end, you do have a buffer if it comes down to it. By restricting yourselves or having the outdoor facilities come later. You have €3000 per m² + €110,000 for the basement, right?

Since I cannot reliably expect bonuses, incentives, or special payments, I do not include them. Thus, for ME the project with the given numbers would be significantly too high.

Especially in sales, things can quickly go either way...

Do you want to have children? Will a salary ever be lost? Can you afford to maintain the house with one salary for a year? Those would still be topics to check off.