Heating Concept Air-Water Heat Pump Single-Family House 2 Persons - Offer from Heating Technician?

Energy consultant:
Can only calculate energy, but cannot design a heating system. For the demand calculation/design, you of course also have to specify temperatures - 08/15 everywhere 20 degrees are used. Then you rather take 22 degrees in the living area and 24 degrees in the bathroom.
And as low a flow temperature as possible - a good standard is 30 degrees with 26 degrees return. Better insulated means even less. And heating pipes are also available in different sizes. A heat pump likes a high flow rate, so take at least a 16 mm pipe. Pipe spacing also plays a role, of course. It should not exceed 10 cm. And also the length of the heating circuits.
None of this can an energy consultant provide you with.

Therefore, I recommend you search the internet for Ing. Heckmann. He is also highly recommended in another community that deals with building technology (you can find it very quickly...).
He is basically THE expert for DIYers (who then like to take a Panasonic Aquarea (but just as a side note) and build it on their own), who deal intensively with correct planning.
He can also provide you with a tailored letter for waiving ERR.
The total costs are transparent and only a few hundred euros. No comparison to possible savings on heating costs and of course less material effort with ERR (no material, no installation, no additional electrical work).

As I said - the floor plan is set,

Be careful, bothering the heating engineer with many questions and foreign planning can lead to them quitting. That happened to me.
But under certain circumstances, that's not the worst thing if it happens.