Heating/Single-family house new construction/ which is sensible/ costs/ benefits for 20 years

...If the architect is supposed to do the exact calculation for the actual demand, he wants 1000 euros for it; with the calculation, I can then go to the heating installer or wherever and have them set up what costs what and what the ongoing costs are.

Just for this detail, that is a bit excessive; in this order of magnitude, the overall planning costs for clarifying the essential key points for a "normal" single-family house. However, here the building geometry etc. is completely unknown, therefore subject to reservation. Whether the architect has the necessary MEP (mechanical, electrical, plumbing) knowledge/training for this, I cannot assess. Leaving the required calculations to a general contractor, I consider hardly effective, as sales interests are often the focus here. Occasionally also professional deficits. One is well advised to engage an independent MEP planner who is not connected to the object and sales-independent.

Best regards