Realistic financing opportunity?

[TIGHT SITUATION? On paper, yes. But actual income is at least €1200 higher per month & special payments like Christmas bonus, holiday pay, Baukindergeld are not yet included, as they are considered as special repayments.]

The bank probably doesn't care about that, since you don't want to enter the contract together. So, his income remains. Is the child benefit paid out to him? Otherwise, you can assume that the bank will not grant a loan amount much above one hundred times the income. In other words - you probably have to be included in the contract. I also don't quite understand the reasons - why does your secondary self-employment jeopardize your financial future? It doesn't bring in much. Your idea with the "Scandinavian model" - cheap financing instead of renting, sale firmly planned & price increases factored in - might not fit well currently either.

Turnkey. Notary and real estate transfer tax included. We can still set aside 10,000€ for interior fittings. I had already explained that.

Then the additional construction costs are missing. They were actually mentioned. Accordingly, another 25,000-50,000 will be added. Additional construction costs have to be paid by the builder.

If that is the offer in the screenshot, then you have surely calculated enough buffer. However, our skepticism or "ok" won't help you at all if the bank does not approve the money for you. Your income from November does not count yet; only the official balance or income from the last three salaries counts. Could relatives help you out with equity?

The house in the screenshot is already narrow. 4.7m I roughly estimated. But why not?

Additionally to be purchased are a garage and an outdoor parking space at €21,990.00 each. If you interpret that strictly, do you HAVE to buy them?

Is it even possible to get a loan for 35 years at the age of 38?
Isn't it the case that the loan can only last until retirement, meaning until the age of 67?

It is possible. But probably only with a 20-year fixed interest period, and that could be the problem/risk.

I am almost 42 and my wife is 38, and we will also take a KFW 55 (10 years) and an annuity loan over 30 years. Kfw 55 will be paid off after 10 years and then the ING will be increased by around €350. Then, with special repayments, we will have a loan term of 20-25 years.