Evaluation of financing new construction - dream or feasible?

Why does the house have to be so expensive?

If a second child comes along and the income decreases, that would be much too tight for me.

For me, a solid deal.
You can take the term like this, even if you want to retire at 60 and still have an outstanding debt of €100k, a payment on that would be negligible (at 5% interest + 5% repayment only €800).
Whether €4,000 monthly (+ bonus and third salary, operating costs for the house estimated at €500) is enough for you to live on, you have to decide. The average family wouldn’t know what to do with all that money.
Together you have almost €100,000 net per year!!! That is absolutely upper class, and if you can’t afford it, then who can?

Good income, high rate with hardly any repayment. This is primarily designed for special repayment. Would increase the repayment. Deductible interest on taxes? But not in Germany for own use. And income abroad does not mean taxation abroad.

Good income, high rate with little repayment. This is primarily designed for special repayments. Would increase the repayment. Deducting interest on debt for tax purposes? But not in Germany for owner-occupation. And income abroad does not mean taxation abroad

Income in Luxembourg means taxation in Luxembourg despite residing in Germany. Fortunately, this was decided in a double taxation agreement in the mid-fifties. Since property prices there are extreme, the state introduced this possibility of deducting interest on debt. We could then benefit from that.

And whether you of course still get anything from the Baukindergeld if you start building now is also up in the air...

Is the pot limited? Yes, then it could indeed become tight. In terms of income, it should work out, as the KfW bases it on the average of the penultimate and the year before last.