Which type of construction suits us well?

Forty years ago, the "prefabricated house" already outshone the "solid house" in terms of thermal transmittance value (even at half the wall thickness!). But even today, your budget expectations rather do not suggest wanting to play the energetic avant-garde when building a house. The additional costs are pretty much eco-label-like.

Aren't most "prefabricated houses" automatically so well insulated that KfW 40+ can easily be achieved through central controlled residential ventilation and photovoltaics + storage?
That means 25k extra for technology, which is subsidized with 15k and reduces heating costs to zero?!

I've seen it more or less the same way so far. Neglected maintenance costs for the technology. But I want it a bit more precise, so I'll consult the [Energieberater].

Aren't most "prefabricated houses" automatically insulated well enough that KFW 40+ can easily be achieved through central controlled residential ventilation and photovoltaics + storage?

Probably not, otherwise many house providers wouldn't offer a different wall construction for KfW40 - others probably manage it solely with supplementary measures. This likely has to do with the fact that the target exists in the realm of theory.

That means an additional 25k for technology, which is subsidized with 15k and reduces heating costs to zero?!

That’s exactly what the thirty silver coins in subsidies are for: so that one does things that would otherwise rightly be thought to make too little sense. There is always a Judas coin for a betrayal, in this case the one against one’s own gut feeling that it is nonsense (or at least not convincingly worthwhile).