Stomach ache due to these large home financing numbers

Yes, although I see the biggest chunk with the house connections, where I would estimate around 15,000 euros.

As I said, the matter with the house is still 1.5 to two years away. Our primary question is whether we buy the plot of land, which we like very much, or have to say that overall it's "too much." Therefore, already a bit of the mental game-playing with the house.

Planning, structural analysis, construction supervision, etc. are involved. According to HOAI, my father calculates "saved costs" of around 60,0000 euros

Well, with the size of the house you are planning, it would have to be a luxury execution to get to 60k; your half seems much more realistic. But it doesn't matter. The bank will tell you what they accept as equity loan.

Otherwise; why shouldn't you buy the property now? The only thing is that with your equity + 100k you won't quite make it and then you'll have to go to the bank anyway, right?

Yes, I also think that half is more realistic, especially since my wife and I do not want an extravagant house, but something fundamentally solid. We will also look into whether, despite the mentioned EL, a prefabricated solid house might be cheaper.

The situation for us is that the house construction will take place 200 kilometers from our current residence. If all goes well, we can live in the house in about two years, as we naturally want to be transferred regarding the workplace, which is not something that happens overnight. Autumn 2019 is achievable.

However, we are faced with the problem that the land situation in our desired location is becoming increasingly difficult despite the rural character there. The plot of land we found represents "one of the last of its kind" in the town; there are not many of this quality left there. The town itself is currently designating a NBG again, but only with plots between 450 and 550 square meters with significant disadvantages (proximity to the highway, power line). Our second problem is that the owner of the plot is relatively ruthless. He is not dependent on the money and makes the land more expensive year after year, as he repeatedly adjusts the purchase price upward according to a five percent (!!!) hypothetical capital interest rate. The plot is indeed beautiful, but relatively expensive at about 155,000 euros for the rural area. It has therefore already been on the market for about seven years. Most potential buyers are deterred by the high purchase price. A year ago, someone offered 140,000 euros, but that was too little for the owner. Now he has raised the purchase price again. Ergo: The plot keeps getting more expensive, and in two years we would already be talking about around 176,000.

As you already said: Our interest-free loan and equity together are not enough for the plot and additional purchase costs, which is why we already have to go to the bank. We simply lack an alternative regarding the plot despite intensive searching. And the plot has really won us over.

If the property is significantly better for 155,000 EUR than the properties in the NBG, then where is the problem? Then it is worth its price for you, isn’t it? But first clarify buildability, etc.…

So with your planned house size, it would already have to be a luxury version to reach 60k; your half seems much more realistic.

Do you think so? With about 350k eligible construction costs, fee zone III, 3/4 rate, you actually end up at about 55k according to HOAI 2013. With a targeted living area of 180 sqm, you come to about 1950€/sqm, which rather points to simple equipment. I would rather calculate with 2100€/sqm...

However, what I wonder is, doesn't the structural analysis have to be approved or calculated by a certified structural engineer? Or is it "allowed" in principle by anyone who feels qualified to do so?!

I think we can disregard the financial situation. Father is an entrepreneur and will provide additional funds if necessary.