House construction financing approx. 185 m2 living area. Is cash payment possible?

With such high equity, I would also try to manage without a bank loan. That also saves notary and land register fees. Is a KfW subsidy still planned? With the grant option, some money would then flow in, which could be used for the outdoor facilities. If the money is still not enough, one could consider private loans from family or acquaintances. They shouldn’t be large sums. Or via product financing, such as 0% financing for the kitchen, furniture, etc., to have money left over for the house.

The structural engineer might still have to plan for a beam. But 30,000 euros for the structural engineering ?!?!?

No, also for such windows and everything around them… exterior walls and interior.

For incidental construction costs, I would assume a maximum of 25,000 euros.

Yes, we still paid that in 2013 …

The earthworks on relatively flat ground can’t be that expensive. For the architect’s planning, I’d estimate about 10,000 euros.

Very naïve thinking.
Yesterday I saw and answered a thread about the calculation of incidental construction costs. Maybe inform yourself in that thread about what all is coming your way.
Otherwise: if you have a different opinion, of course you can try. Just start. If we are right and the money isn’t enough, you can continue building after obtaining financing.
But then I wonder why you’re asking here.

do you want to outsource everything?
the turnkey construction price index in July 21 was at 3500E/sqm.
with own contribution, it is quite conceivable to be able to map that, especially if time does not matter.
the prices of materials will not remain permanently at a very high level, but you won’t get back to the "cheap" pre-crisis level...
you can basically just start, and if at the end there is still work left over from the money, you can always find a bank to top up the rest for you based on the equity ratio. but I would at least consider a KfW loan with appropriate funding. that is wasted money and it would completely take the pressure off you.

We have three appointments with different GCs coming up. Let's run the numbers for the house. I will report...

I can hardly imagine building a house without a basement for this amount.

Then why are you even asking? Believe the people here calmly, most of them are already ahead of you. And, sorry, your list of features definitely does not indicate the possibly still feasible lower standard, so the tone here is very clear and accurate.

I would not invest all the equity. Money is cheap at the moment. It makes sense right now to invest a part of the equity with a focus on returns. This does not mean that only a small amount of equity should flow into the construction project, that is also an investment. But ich would invest a certain percentage in other forms of investment.