Decision for a heat pump

I have now looked at our gas consumption over the last 17 years (1 invoice is missing)

It actually tended to decrease even though there were no major renovations or changes to the heating system.

Does this explain the high heating load?

Regarding the question of why the heating is defective: It keeps malfunctioning, and the heating specialist said that repairing it is no longer worthwhile, especially if one is already considering getting a new one.

One more stupid question: can I counteract a (slight) oversizing with a slightly larger buffer?

Another idea that could explain the high consumption: At least 300-400 liters of hot water at 60 °C are used per day. What proportion does this have on the heating capacity?

Another dumb question: can I counteract a (slight) oversizing with a slightly larger buffer?

The expert would slightly undersize and omit the buffer.

Another idea that could explain the high consumption: at least 3-400 liters of hot water at 60 °C are used per day. How much of the heating output does this account for?

If you heat 400 liters from 10° to 60°, that's about 20 kWh. Or 7,000 kWh per year. Based on the 32,000 kWh you mentioned, that's roughly 1/5. By the way, that's 3 generous bathtubs. Every day. Do you have a hair salon or something similar?