Air-water heat pump in KFW55 house / heating load, standards?

Then I would not place too much weight on the energy consultant's calculation if he uses an incorrect value for something as fundamental as the NAT.

Has he taken the controlled residential ventilation into account in his calculation?

I strongly advise you to have it calculated externally, see the linked thread.

The 5 -er heat pump should generally be suitable in terms of performance.

Thank you. Yes, I think that is a well-invested 300EUR.

Did he take the controlled residential ventilation into account in his calculation?

I don't know currently, probably not. Otherwise, how would you arrive at 8KW.

There has already been a case here where the subcontractor backed out because he didn’t like it

Yes, that was with me, the standard subcontractor of my general contractor. He got more and more monosyllabic with my questions, and when I asked if he would execute according to external planning, he wrote without comment that he would not carry out my project.
By now I'm no longer upset about it, since my neighbor, who is building with the same general contractor, is also just annoyed by that subcontractor.
Yours seems at least to be easing up now. But prepare for additional costs, because the closer pipe spacing leads to more effort and material.
It could also be that the pump capacity eventually won’t be sufficient for the longer pipes (that was the case for me). Then we had to increase the hysteresis, and at NAT -12 I no longer get below 30° flow temperature. But I only have the Energy Saving Ordinance, nothing better.

I strongly advise you to have it calculated externally

Look for IB Heckmann. It is comparatively inexpensive, fast, and seems to calculate fairly correctly, although I cannot verify that.

I am convinced that you will come under 30 degrees in practice.

Searching for IB Heckmann. It is relatively inexpensive, fast, and seems to calculate somewhat correctly, although I cannot verify that.

I can confirm good experiences. It carries out room-by-room heating load calculation, heating system design (underfloor heating including laying plan or also design of radiators) etc.

I am convinced that you will get below 30 degrees in practice.

Yes, that only applies at -12 then. We ourselves only had a few nights like that this winter, which really was cold again.