Is financing feasible? Single-family house 155 sqm

I believe I paid significantly more than 3000€ for water and wastewater connections. You have two items here, one for the supplier and the other for the necessary civil engineering. Just the shafts for wastewater and, in my case, also for rainwater cost more than 3000€. Only the civil engineering - the supplier charged extra.

Well, that's not entirely correct. The public utility providers calculate flat rates, probably the same for you. Wastewater is excluded. It now depends on the negotiation skills of your site manager what discount you get for your own work. So the new water connection was certainly cheaper. But as I said, negotiation skills are also required here. In some regions, gas is added as well.

This (and some other) thread/s is quite clearly the reason why I don’t seek a second opinion here on financial topics.

1) Income is generally doubted
2) Consumption behavior is generally doubted
3) One is generally too young
4) One is generally too old
5) With children, one can generally no longer earn money

Now to the OP:
Your writing really comes across as somewhat know-it-all. Especially regarding the assessment of construction costs, I would put in a bit more work. There are one or two great threads here (house construction almost always costs more than expected) that examine this issue.

Maybe an extra buffer makes sense here to avoid ending up with an expensive additional financing later.

And then a very personal piece of advice from me: Play through the scenario of a separation and consider how you want/can handle the debts in that situation and preferably document that in writing. We are 26 and 23 (but with two children) and have gone through the process as well.

I’m keeping my fingers crossed for you.

If you continue to push forward with the construction project, we of course look forward to further information (floor plan, construction progress, pictures).

This (and some other) thread(s) is/are clearly the reason why I don’t seek a second opinion here on financial matters.

1) The income is fundamentally doubted
2) The consumption behavior is fundamentally doubted
3) You are fundamentally too young
4) You are fundamentally too old
5) You can fundamentally no longer earn money with children

You are already the second one blowing this horn. The thing behind the story here is that what the OP assumes is against the civil service law. Of course, it may be that the girlfriend gets promoted. But no one (!) can give her a guarantee for that. It has been ruled by the highest court according to which criteria civil servants may be promoted. These must first be met, which at the current time they are not (can’t be). This is not tragic in itself, maybe everything will turn out well. But it shows how naive the OP is approaching the project. He can do it, that is the privilege of youth to allow oneself that without self-doubt.

you are now the second person to blow this horn. The thing behind the story here is that what the OP assumed is against civil service law.

So what? – Am I not allowed here as a pimp to ask for a second opinion on whether my financing calculation works out? – just because I named my salary as managing director of the Miranda Bar "A13" (because it just happens to correspond to that amount) without having read up on civil service law beforehand? – Where is the problem in simply assuming a salary X or a wage Y as given? – It can’t be that one has to scan their tax assessment here in order to be allowed to ask a question!

Even though the choice of words here is sometimes very harsh, the main point is probably to make the OP aware of these risks. And yes, here almost regularly a nice project is talked down or underestimated financially, but there are usually reasons for that, even if they may be somewhat exaggerated in the presentation.

Apart from the specific topic, I see here an OP who first timidly asks whether it can all really work out and then, at the first expressed doubt, confidently explains at length why everything is great. My clear recommendation: Do it, don’t ask!

(I’ll spare the comment about odd-toed ungulates vomiting in front of the medical store, but I do notice that in times of Corona, “watertight” plans suddenly spring leaks – incidentally also in the area of civil service law.)

So what? – Am I not allowed here as a pimp to ask for a second opinion on whether my financing calculation works out? – just because I named my salary as managing director of the Miranda Bar "A13" (because it happens to correspond to that amount) without having read up on civil service law beforehand? – where is the problem in simply assuming a salary X or an income Y as given? – it can’t be the case that you have to scan your tax assessment in order to be allowed to ask a question here!

see my last paragraph. no problem in itself, but reveals a fundamental problem of the original poster. none of us really care what he actually does; that is his own decision. but if he asks for opinions, he will get them. if he only wants a yes or no as an answer, I recommend creating a simple survey with exactly those answer options. so, I’m out.