New construction KFW55 house - heating design, different statements

From my own experience, I can say: weigh the argument "Schallemission" heavily! Our heat pump is quite loud, and I have now lowered the frequency so that it does not run at full load as often.

Personally, with my insights, I would now consider a groundwater heat pump. Especially in colder areas, it is more efficient than an air-water heat pump.

Otherwise, I have heard or rather "not heard" a Viessmann at full load. This manufacturer would be my favorite.

Always choose the company where possibly friends and acquaintances have had good experiences. Our fitter is now banned from the house.

Have an external office calculate this for you.
Room-by-room heat load calculation
No buffer, no mixer
Flow temperature 30 degrees or less
Connection of the HKV large enough
Pipe size chosen large enough 16/2 17/2
Bathroom possibly wall heating.
OWL had this calculated by an office, they did a good job.
Find a heating installer who accepts an externally calculated plan,
See the problems that Tolentio has.

The questions scare me a bit, although I am a layman myself and do not like to deal with technology.
What will become of the future tenders? :eek::D
Regarding your questions:

and even worse, everyone thinks their technical implementation is best.

Every company (not only heating) describes THEIR technology or implementation as the best.

a fresh water station is absolutely necessary to prevent legionella"

Fresh water station? I have never heard of that. There is surely also a legionella program for air-water heat pumps?

drinking water storage must be at least 300l

Yes, but that should then also be sufficient. It doesn't have to be bigger.

In the bathroom, you need an electric supplementary heater

That depends on the size of the floor area. You can’t say that as a general rule. If the bathroom is quite small (roughly 5-8 sqm), then the bathroom might have difficulty getting warm.
A towel radiator does not heat, especially if it is covered with towels.

however, you must comply with the necessary sound pressure limits for night operation.

I would probably follow that, and also take ’s suggestion to heart. I would generally reject the most expensive one; I have never heard anything bad about Viessmann.
All should be heated.

Fresh water station? I've never heard of that. There must also be a legionella program for air-water heat pumps, right?

That is a totally common water storage tank. Separation of the heating circuit from the potable water circuit. The water storage tank is heated by the heating system. Inside is a heat exchanger that warms the fresh water flowing through. No legionella, since there is no potable water storage tank. Great thing, but a bit more expensive (should cost around €1,000-1,500 extra).

Our technician is now banned from the house

What did he do to your heating system? Or was he in bed with your wife? :-p