Decision aid for choosing the construction company

With KFW40+ it is probably much more difficult. But there are also regional carpenters who are not represented nationwide.

KfW40+ is probably massively more difficult. But there are also regional timber builders who are not represented nationwide.

Oh right, I must have overlooked that - then it really gets more difficult.

Otherwise, again @TE:

Are there reasons why you absolutely want to build KfW40+? I know that from my own experience. At the beginning, we were also completely fixated on it – now we are building KfW55. Just as a "tip" or info on the side. KfW40+ is definitely not a mistake!! In connection with your ideas and possibly looking at the options with regional massive general contractors, it’s just difficult. Maybe you’ll reconsider it or something.

KfW40+ is economically difficult to represent... you can hardly recoup the additional cost over a long period.
Photovoltaic system should be purchased separately and not through GU. I have already read incredible prices in the forum here.
I paid 12k for material for my 21.6 kWp.

If you definitely want a timber frame house, then clearly, in the end only the prefabricated house industry remains available nationwide.

There are regional providers for all construction methods - they are just not widely available.

Believe me, a provider’s image is totally deceptive...

After all, that is essentially the main job of an image ;-)

Okay, thank you very much for the many answers. I had already feared it. All fixed plans will be put back on the table for review.
So.. about the topic KFW40 Plus. We simply want that. Out of conviction. There will certainly be enough reasons against it, but certain cornerstones have to be set and this is one of them. Whether that is smart or not, it doesn’t matter, we want it, even if it might cost more. It is correct that this also rules out many solid builders, but Viebrockhaus, for example, would be possible.
I am aware that this forum naturally teems with experts and people who know their stuff, I am not one of them. I want, as stupid as it sounds, simply to build a house. I am aware that there are always possibilities for optimization, you can always save or do something better, otherwise I wouldn’t be here either, but overall I am clueless and do not expect that every component will be selected by me manually. I do believe that the mentioned companies build solidly so far and you don’t do everything wrong with them, right? I don’t know many regional providers around Frankfurt. Streif Haus, Rensch-Haus, Finger, they are like that here, but all are “under” the ones mentioned, as far as I read.
I am also aware that websites and impressions can be deceptive. That is the point.
I sat down yesterday, looked at the wall construction of Kampa, Weberhaus and Büdenbender and thought: okay, what is really different? Everyone says the wall is the best, throws around values. One has a vapor barrier, the other only has gypsum boards (Büdenbender). How can that be? Büdenbender advertises that. I lack the expertise to say, yes that is good. On the other hand, I think they don’t build crap that ends up molding? Kampa has the vapor barrier on the outside of the wall, Weberhaus inside. With Weberhaus you would hit it when drilling into the wall, then what? Is that bad? Why is it like that? Or does it just not matter in the end?
So.. do you understand what is bothering me now? Somehow I think they don’t build crap, but, for example, this thing with the walls and the barriers is currently an issue for me and I have no idea whether it is relevant or not. Can someone say something about that, for example? Or is it a religious war? Am I too naive to believe that they already know what they are doing?

Somehow I think that they wouldn't build junk [...]

Without any reference to the home builders here: But at least since the diesel scandal, it should be clear that even global corporations can get away with deliberately selling junk for a long time.