Is financing without equity realistic?

And now all of a sudden you are willing to restrict yourselves?

It has nothing to do with restricting but rather that now the 500 euros are simply not spent on any nonsense. Or rather, that our quite expensive car is paid off (45000 euro purchase price).

Our acquaintance completed his house this year and needed 190,000 for just under 200 sqm with everything included

That means he needed about EUR 950.00 per sqm. That makes EUR 228,000.00 for 240 sqm. That would be about 12% more than what you have calculated so far.

[*]Earthworks
[*]Canalization works
[*]Basement (basement alone up to the top edge of the basement ceiling see own construction phase Basement Building)
[*]Load-bearing exterior masonry
[*]Load-bearing interior masonry
[*]Floor slabs
[*]Concrete floor stairs
[*]Roof truss and roof insulation
[*]Chimney with chimney cover
[*]Non-load-bearing partition walls
[*]Roof covering
[*]Tinsmith work (plumbing work)
[*]This is included. For the interior finishing heating, windows, sanitary, etc. Our acquaintance completed his house this year and needed 190,000 for just under 200 sqm with everything included

Why basement? I think you are building without a basement? And all that is supposed to cost €50,000. Ambitious, ambitious. By the way, I hope you didn't use the prices on the linked page as a benchmark, because it is no more than a guideline (actually not even that). I also looked at the page, but then gave up because it didn't even come close on most things.

... honestly, there hasn’t really been a good reason to save much so far

... our quite expensive car has been paid off (45,000 euro purchase price)

There are people who spend what they need, and the rest is saved automatically. And there are people who just spend everything that is available.

Both have a right to exist, but the second group will find it difficult to keep money together permanently and consistently.

I understand the frustration of paying high rent and “getting nothing out of it.”

Still, this is once again the classic case of wishful thinking without any realism: incidental construction costs are not taken into account at all (permits, etc. and supply services are supposedly all free), a breakdown of actual costs is only roughly estimated (although a professional mason should know better), a neighbor/acquaintance is simply named as a positive example (here conveniently rounded up), and then of course over 200 sqm with double garage and basement or not?! (after all, you only build once).

Just break down how much it saves if your husband pitches in or does a lot himself — after work, mind you. I can imagine that a lot can be saved, but the materials for everything still have to be paid for.

Then maybe realize that even a mason can get sore — building on the side for another one or two years can wear down even the toughest ;)

What does the brother-in-law say, with whom you live with 5 people, about a permanent construction site? Could this arrangement possibly be crisis-prone???

Then realize the kids’ age: how old will they be when you move in? Will they possibly do their apprenticeship in another town — so is over 200 sqm (with or without basement) really necessary?

You will have a permanent construction site of your own for 3-4 years. I don’t believe a bank will finance you 100%. It won’t just hand you 200,000 to spend however you like at the hardware store!

I don’t even want to start on financing with child support from the ex.

Maybe the beginning of the dream of your own house is to already start working full-time?! :D

In my opinion, it is not realistic. You don't have any savings rate at all. The maintenance payments will eventually stop and then? Do your children pay you rent? If not, what happens then?