Single-family house: Is the rate realistic? How much house can we afford?

Besides, you are sugarcoating your salary increases. The roughly 300 EUR more per month are currently just about an inflation adjustment

I agree. Unfortunately, the increase in net income will not be felt to the same extent because everything keeps getting more expensive.

Oh, one more thing: If I only look at our monthly net salary and take ⅓ of that, I end up with €2,100. So even according to the very simple and vague rule of thumb, I wouldn’t be far off from €2,500 ... :)

When there is still a month left at the end of the money, €400 is a really high amount...

but with his family income and planned children, he should keep the rate under 2k.

Are you sure that's a good idea? Of course, you can drastically lower the repayment. A €500,000 loan at 4% interest and 1% repayment has a term of 40 (!) years with still almost €2,100 per month. One can have a long discussion about the sensibility of such a long duration extending beyond retirement. In any case, this is miles away from your previous advice:

wenn möglich nicht länger als 20 Jahre

Are you sure that’s a good idea? Of course, you can reduce the repayment extremely. A €500,000 loan at 4% interest and 1% repayment has a term of 40 (!) years with still almost €2100 per month.

One can debate for a long time about the sensibility of such a long duration extending beyond retirement.
In any case, that is miles away from your previous advice:

Ideally, you can do both, only 1/3 of the household net income and repay it in 20 years. And then we’re back to €9000+ net income. When we bought our old building, our notary pressed upon me during the notarization of the land charge (which was 100% financing) that such a real estate financing should be completed within 15 years; we managed it in 12 and then had the equity for the new building.
If the financing runs into retirement, one should perhaps be aware that one will no longer live in this house during retirement but will sell it beforehand.
We lived in the old building for 12 years, now for 5 years in the new building; one can also change owner-occupied houses...

Ideally, you can do both, only 1/3 of the household net income and repay it within 20 years

And in reality, this is currently only possible if you have a lot of money. The top 10% by income probably won't be enough; it has to be more like the top 2-5%. So we're talking about an ideal case that is practically not applicable in reality. Either you tighten your belt and live a bit more frugally, or you extend the financing period. Unfortunately, your prices are absolutely far from the current ones, now with higher interest rates.

We have at most a weakness for our hobbies - espresso machines, bicycles, home cinema

I don't even want to know how the kitchen planning will turn out cost-wise with the hobby "espresso machines".... It’s best if you buy a built-in espresso machine, then you can "skip" this hobby. Bicycles, including good quality e-bikes, easily reach >€4000 and thus more than the value of a used Opel. There was also a rule of thumb in the FAZ some time ago: you should invest 10% of the car’s value in the bicycle if it is a hobby mode of transport. (I also stuck to that.) Home cinema requires a lot of space (drives up construction costs) and for high-end sound systems the price scale is wide open upwards.