New construction or existing property financing plan realistic?

Is there any reason to hesitate for a moment and not pay off this loan immediately? Provided that the prepayment penalty < interest until repayment

No, you are right, there isn't. The payoff will take place this month.

With two children in the household, there is a sibling bonus of 10% until the older one is three years old. Thus, the maximum amount of 1800 EUR becomes 1980 EUR.

And in case you’re wondering why I converted €2,100 repayment into €2,500 savings with a stroke of the pen. That is the "I REALLY want it surcharge," commonly called a safety reserve.

Just because you haven’t saved in the past doesn’t mean you will continue that lifestyle in the future.

Objection, Your Honor:
Unfortunately, humans are creatures of habit. And reducing expenses is harder than increasing them. The entire Schufa is based only on probabilities, ...Rich Dad, Poor Dad...
I know enough people who say: Yes, if I have to, I can. But unfortunately, they’re still living in an overpriced rental apartment in their mid-40s or have a forced auction on their record.

It certainly requires some discipline, but it’s not impossible.

Definitely not impossible, show me for one year that it works and how you feel about it.

And even if it doesn’t work. That’s neither good nor bad, just different. But then it doesn’t necessarily have to be your own house. The €400 is the net plus (rather €800 - 1000) to reconcile your previous consumption habits and the house. Sounds odd, but that’s how it is.

And if the €400 monthly safety is saved over 5 years and the €10K bonus has gone into special repayment (after building the house), then in the future you can gladly put half into consumption.
And 5-6 years go by very quickly with children. How do I come up with that? ;-)

The conditions for your own house are still good. Really adjust a few control knobs. And good luck with that.

It's not difficult to reduce expenses:

[*]You just don't buy brand-name products anymore
[*]Ride a bike or take the train instead of driving
[*]Cancel expensive contracts
[*]You ask yourself with every little gadget whether you really need it or not...

I see it quite concretely with us. There are still the old expensive contracts running that you don't have on your radar anymore, club memberships that you don't really attend anymore.
Only buy organic products (which I think is good, but unfortunately usually expensive).
I had always downplayed all these things before, but now that it’s getting serious, it can’t continue like this.

Also, 6k net income, when both work full-time even more, how could you not be able to afford a house?

Also 6k net income, even more if both work full-time, how could one not afford a house then?

You just have to really want it. And so far I find the OP's attitude lacking. So check twice before you commit forever...

In my opinion, with these conditions it can be done within 20 years without major cuts in quality of life. I just point out that he shouldn’t continue as he has been.

I am more from the "work hard, build a house" camp. But there are certainly people for whom that’s not their thing, and who feel forced by "external circumstances" to do otherwise. This difference is neither better nor worse. You just have to make an active decision and be consistent.

...but now that it’s getting serious, it just can’t go on like this anymore.

True.

It's not difficult to reduce expenses

Crap. When you list it like that, there are still a bunch of things that are also quite simple: quitting smoking (stop smoking altogether), losing weight (eat less, move more), regularly decluttering/cleaning/tidying up, etc. Sure, there are people who just do it, but that doesn’t mean it’s easy. But to contribute something useful: we use a budgeting app (YNAB) that has helped us tremendously in increasing our savings rate. Unfortunately, all the good ones come from the USA. The ones based here all only allow you to track what you spent on what, which I find too limited compared to a forward-looking approach.

Trash. If you list it like that, there are still a bunch of things that are quite simple too: quitting smoking (smoking no more), losing weight (eating less, moving more), regularly decluttering/cleaning/tidying up, etc. Of course, there are people who just do it, but that doesn't mean it's easy.

But to add something useful: we use an app for budget planning (YNAB), which has helped us enormously in raising our savings rate. Unfortunately, all the good ones come from the USA. The ones based here only allow you to track what you spent on what, which I find too limited compared to a forward-planning perspective.

The examples I gave are undoubtedly easy to implement. What's so difficult about that? As long as it doesn't affect your comfort zone, it's all relatively easy to implement. Ok, I wouldn't want to take the train either ;) I'd rather ride a bike.

I know it myself. Off the top of my head, I can think of 3-4 things like mobile phone contract, electricity provider, car insurance, Unitymedia TV that I don't use but still pay for. Many people are probably the same, once you get used to a certain lifestyle, you don't question these things.