Are the construction costs listed correctly?

I would really reconsider the no-ventilation thing, especially with the highly insulated houses nowadays..

and we are also building with an architect, I would never trust myself to do all the tenders etc. because more information belongs in it sensibly than one can oversee oneself.
you could at most consider continuing with a general contractor, but keep your hands off doing it yourself!

If doing it on your own: do you have experience or someone in your circle of friends? Alternatively, a lot of time.

We worked with our architect up to phase 5. Additionally, he also put the shell construction out to tender for us.

We are doing the rest ourselves or have already done it. However, only because my dad is a professional.

Moreover, most of the trades are within our family and circle of acquaintances.

Yes, that's what I meant by that. My acquaintance does something similar. However, it has been ongoing for a long time and involves considerable effort.

Thank you for the info. I have just been toying with the idea of possibly doing it myself. But I have to say, my knowledge is limited. I do know one or two craftsmen, but well. So I'll just leave it at that. The costs, especially for performance phases 5-8, are already considerable. Ventilation will not be included. Neither my wife, the architect, nor I are fans of it. Such ventilation systems also do not have the best reputation. But everyone has to decide that for themselves.

Ventilation is not included. Neither my wife, the architect, nor I are fans of it. Such ventilation systems also do not have the best reputation. But everyone has to decide that for themselves.

I see it that way too; everyone has to decide that for themselves. With many KFW-XX exterior wall constructions, it will be difficult to consistently ventilate all rooms independently. We have a 36 cm pumice stone, which fulfills the Energy Saving Ordinance. It is not highly insulating. Regular ventilation is completely sufficient. Then, for example, in the bedroom, lime plaster and you have an excellent indoor climate.