So,
from the advice received and what I learned from it, it seems that the most appropriate course of action is:
- Insulate as much as economically viable.
- Ensure good airtightness of the house
- Use mini splits
- Use Solar PV to assist minisplits in summer
- Use gas to to assist minisplits in winter.
Did I get it right?
Minisplits are definitely the easier and cheaper option up front.
I had them installed in previous houses and it only takes an afternoon to get them retrofit, in a new install it might even be easier as the electrical and plumbing can be worked out in advance.
What I have against them in the noise they make and the seem to waste a lot of energy (a lot of heat is produced by the external unit).
I was sort of sold to the idea of hydronic floor heating as a sort of quite and ecological way to get warm in winter, but I might have to give up that idea.....