Financing land and house construction

Addition: The biggest risk is still the refinancing in 15 years, which could become unpleasant if there is a sudden increase in interest rates at the wrong time. However, this can at least be minimized in due course through [Forwarddarlehen] as well as by simultaneously saving assets with discipline (not everyone can do this, but not everyone needs forced savings, even if this is so eagerly preached here in the forum).

Addition: The biggest risk is still the refinancing in 15 years, which could become unpleasant if there is a sudden spike in interest rates at the wrong time. However, this can at least be minimized in due course through forward loans and simultaneously building up assets with discipline (not everyone can do this, but not everyone needs forced savings, even if this is so diligently preached here in the forum).

I see it the same way. Existential risks of the main earner are accordingly covered by insurance. Otherwise, after 10 years, we will of course take a look at whether we should refinance using the special termination right and secure an attractive interest rate (if available). I feel much more comfortable saving a buffer outside of the loan rather than putting it directly into repayment of the loan. Accordingly, after 10 or 15 years, we will hopefully have set aside quite a bit to reduce the residual debt when refinancing.

Unemployment (or even just a dismissal) cannot be insured, and disability due to occupational reasons will also be a difficult endeavor at the required scale here. In this respect, insurances obviously help, but unfortunately not every risk can be insured. But that's just how life is. I consider a higher repayment rate to be significantly riskier, as even slight income losses then become a problem. Better to save more privately, but unfortunately forced savings have legendary status here. Some people need that, but ultimately it has to be considered individually. Those who earn 6-7k net should generally be able to handle money (exceptions especially from the celebrity area confirm the rule).

Our monthly rate is €3,375 with different repayments depending on the credit component (1.26%, 2.55%, 3.02%).
The residual debt after 30 years is difficult to quantify due to the various components and many variables; roughly estimated about €300k according to the payment plan; in reality hopefully +/- 0 (our personal goal).

So you are clearly below the €4,500 from your initial post. It should therefore be fine, although personally I would still consider it too risky with three children. Unfortunately, in my circle of friends there have been several cases in recent years where people in their mid-40s—in seemingly secure positions—suddenly received severance offers from their employers and could not find comparable jobs afterwards.

where in the mid-40s the severance offer suddenly came from the employer and no comparable job followed.

Then you talk to the bank, put the severance payment as a special repayment on the loan, and manage wonderfully with a smaller salary. Such a situation can also be a personal gain if the new job is poorly paid but perhaps not as stressful (especially with three children, every minute of free time is priceless).