House construction according to the Building Energy Act still acceptable or better KFW55

Subsidies for retrofitting, you will probably not get any more. The magic word is mandatory solar panels on new buildings or roof renovations. Either you install them right now or you leave it for the long term

Then there is simply a subsidy for all who are not obliged. It was the same with BAFA for heat pumps; the subsidy for a new heating system was only granted to those who were not already obliged to replace their oil heating.

If you can afford it financially, 40, 40plus or 55 would certainly be better, also with regard to the resale value. For various reasons, however, we ourselves only build according to the Energy Saving Ordinance.

It's kind of like recommending organic products from the local farm shop but only going to the discount store yourself.

That's roughly like recommending organic products from the local farm shop while you yourself only go to the discount store.

The financial means of customers differ, the knowledge about nutrition, one person is 15 minutes by bike to the farm shop while someone else might take half an hour by car, different allergies and intolerances, etc.. ;-)

Two things are being confused here. Of course, every house today must meet minimum energy efficiency standards. It is perfectly fine to strictly follow the fulfillment of these standards. You don't need any KFW something for that. The KfW standards are primarily funding conditions, which prescribe both energy efficiency standards and ways to achieve them. Anyone who opts out of the funding and goes their own way does not necessarily build a worse and less efficient house. In a resale, the stated KfW standard may be a well-known seal but not a real quality feature that is crucial for the valuation. I consider the tip from very valuable: Build what your building partner often and thus routinely builds. If this deviates from your wishes, look for another building partner.

I consider the tip from @11ant very valuable: Build something your building partner often constructs and thus does routinely. If this differs from your wishes, look for another building partner.

Although I - like you actually also ? - give preference to the "chemistry" with the builder over the "award-winning stone" in case of doubt.

Whereas I - like you actually? - in case of doubt give preference to the "chemistry" with the contractor over the "best test stone".

Yes, that is a basic condition: Never buy from people you don’t like, who give you a weird gut feeling, or who have no interest whatsoever in you or at least your wishes. And before someone comes up with the glorious idea to draw a timely but internally illogical inverse conclusion from that and points out that something can still go wrong, I’ll anticipate that: There is no guarantee that everything will go well – at the same time, there are ways to exert influence yourself – even if it is the choice of contractual partners.