Property, house buying experiences, opinions?

Construction costs: approx. 412K (incl. painter 20K, tiles, sanitary, additional sampling 6K, own contribution: flooring)

For a 160sqm KfW40 house?
I am actually missing desired and partly necessary special equipment, e.g. in the electrical system, where the standard is usually really poor.
In addition, there are quite a few things that are not included in the construction service description. The necessary kitchen etc. was already mentioned separately.

[*]Development costs: 8K water connection, fiber optic
[*]Additional construction costs: 20K demolition, 12K excavation

I am missing the real additional construction costs of 30-50 thousand for rainwater, building application/permit, and all the extra stuff, also construction power/water etc.

I usually stay completely out of financing discussions and will not address numerical calculation questions here either, but: an income with good prerequisites for decent savings performance / loan installments and the financing component KfW funding, which is already deemed necessary by self-assessment, first of all do not fit together ...

Basically, it is supposed to be a KFW40 house, since from our point of view financing is only possible with the corresponding KFW loan.

... and secondly, one must not forget that the KfW contribution to financing is also opposed by additional costs due to the associated efficiency house fat level. The existence of this component in the financing mix may still be useful, but it partly helps with a problem that one wouldn’t even have without it.

Currently, we tend more towards a prefabricated house, since there is at least one very good provider in the region.

That sounds to me like "you still have a lot to learn." Prefabricated houses are only as much "more prefabricated" as lemon butterflies fold lemons, and a second myth often attributed to them (the more precise final price prediction) is a joke with a long beard. At least the third myth (less durable cardboard box) is also false or no longer valid. EH40 is often more easily achieved by the wood frame panelers, but the masons are catching up by now. By the way, among the wood frame panelers, the non-regional providers are regularly also those with the more mature products; the regional idea is more advisable with the masons (and with wall panel masons anyway).

Is this a joke thread?
Forget it for now and save up for a while... in 5 years then...

I can only agree with that. Your savings rate is quite low and should be at least twice as high given the income. It doesn’t seem to be due to the amount of the current rent?

The woman is still on parental leave, with 2 children who are 3 years apart in age she probably didn't work full-time between the births, maybe not at all. And the parental allowance is lower than the income and eventually runs out.

With the alleged savings rate, there has to be more there anyway. Before the children came, they were 30 and 34, so probably not just 2 years in the job but rather 5-10. For that salary, the equity is very low. If there’s no stock portfolio or a valuable classic car worth 100k behind it that wasn’t mentioned, then too much has simply been consumed for the current interest rate environment. But with that salary, you can quickly turn the tables and then take another look in 3 years.

Basically, it is supposed to be a KFW40 house, as from our point of view, financing is only possible with the corresponding KFW loan.

Basically, I don’t understand this sentence. Is that the decisive criterion? Please calculate the additional investment versus the subsidy or interest rate. And whether you really save/use as much energy as is calculated on paper? We built KfW55 and it is almost a break-even game. I recently wrote a bit about our house here. Maybe it will at least help you make the cost side more transparent?