New construction financing single-family house 150 - 160 sqm

What interest rate lock-in period did you have?
I'm currently considering it, because with a 20-year term and 2% repayment, a considerable amount still remains. Maybe it's better to go for 25 or 30 right away.

20.
In my opinion, 20 years is completely sufficient. After that, the risk is manageable. I would have even gone for 15 years, but at that time the interest rate difference was too small (which changed in the end, but by then it was too late). Nevertheless, I think that 20 years is a good period to also be able to weather economically worse times.

Unfortunately, this is calculated in an overly optimistic way, because after the 10-year fixed interest period, the KfW loan is not fully repaid; out of the €120,000, there is still a remaining debt of well over €80,000, which of course must continue to be financed...

Of course, you can make special repayments, but this is not to be expected (the OP has not mentioned anything) and €80,000 is not peanuts...

€66,000 remain --> you receive a repayment grant of €18,000 for KfW55.

If you are "clever" and have financial worries, or would prefer a lower monthly payment, then I would invest the money accordingly for the short term, or simply set it aside and then make a special repayment after 10 years. But yes, you probably won’t get rid of the €66,000 completely; however, this definitely reduces the monthly rate by half.

Exactly for this reason, I would personally split my loan components and possibly include another component with a fixed interest period of 10 years (unfortunately, KfW cannot be repaid early and not repaid over 3%), repay this very aggressively in the first years without children with, for example, 6% or even more, and set the rest as low as possible. This way, after 10 years, you can manage to have significantly lower monthly burdens.

What fixed interest period did you have?
I'm just thinking about it because with a 20-year term and 2% repayment, quite a substantial amount still remains.

A substantial amount from today's perspective... I wouldn't let that drive me crazy.
If you haven't caught the completely wrong collective agreement, the remaining amount on the debt clock should still be easily manageable in 20 years, even if interest rates should be significantly higher then.

First of all: I also think that it is quite doable for you. But a few question marks arise from your information: 1. How is your household income distributed (you/partner)? That is quite relevant for considering the time from the first child onwards. 2. Do you keep a household budget? The numbers somehow give me an estimated impression. How do you arrive at the expenses with 2 children? Just as a small impression: the U3 place for our daughter costs us 620 euros per month (including meal money). We have about 6000 household net income. The more precise the numbers (and many can help very well to assess them here), the clearer the situation will be for you and the fewer surprises there will be.

First of all: I also think that it is quite doable for you.
But a few question marks arise with your information:
1. How is your household income distributed (you/partner)? This is quite relevant when considering the time after the first child.
2. Do you keep a household budget? The numbers give me a somewhat estimated impression.
How do you arrive at the expenses with 2 children?
Just as a small impression: the U3 place for our daughter costs us 620 euros per month (including meal money). We have about 6000 net household income.

The more precise the numbers (and many here can help to assess them very well), the clearer the situation becomes for you and the fewer surprises there will be.

Regarding 1.:
Me: 3.1 k€ net
Partner: 2.0 k€ net

We are not married yet.

Regarding 2.: I do not keep a detailed household diary, but the regular costs are indicated quite accurately.

The expenses with 2 children are only estimated.
620€ for the daycare place is pretty steep...

The expenses with 2 children are only estimated. 620€ for the daycare spot is really steep...

You can already look up the parental contribution rate for your home municipality. In addition, the meal fees of the respective daycare or childminder. With 2 children in daycare at the same time, you pay significantly less or nothing for the second one.