One could remove the wooden facade. Then
- install vertical battens and fill the space with mineral wool
- install horizontal battens and fill the space with mineral wool
- install vertical battens and mount the ventilated facade on them
As far as I know, 6 cm per insulation layer is "normal". That would mean 12 cm in total.
The ventilation gap should be about 3 cm.
Means
6 cm insulation
6 cm insulation
3 cm ventilation
x cm facade
all together then about 15-20 cm total thickness. Depending on what one does/wants to do.
If it is a solid house, it should be relatively easy and inexpensive.
Whether the insulation thickness is really necessary is up to oneself to decide.
Judging by the photo, too thick an application on the roof could be a problem with driving rain as there may not be enough roof overhang (possibly).
For the facade, you can take many materials. Either Eternit, i.e. fiber cement, which nowadays can also provide very nice facades (in wood look, etc.) or real wood or some kind of plastic or...
Personally, I find Eternit a very good material, simple and very durable.
So this method could be looked at more closely.
But. How is the roof insulated? Before doing anything to the facade, one should inspect and renovate the roof. In my opinion, that is one of the most important points in a house.
PS: Unless there is already a fixed plan for renovation, I would only start the work after winter.