Eliminating odors and soot from a house with clay plaster - ideas?

.. mh well I would just drive over it once with the excavator and rebuild it... that sounds unhealthy and very labor-intensive to renovate to me.

Alright, then the complete gutting will probably be necessary. How would you proceed with the other rooms that only smell slightly musty (probably from the general odor in the house) and were not damp according to recent measurements?

I would gut them as well. If it smells musty (do you really mean musty = with an earthy, compost-like hint, not stale or damp?), there is at best saltpeter, at worst black mold somewhere inside. And even if you use something strong on it. After such a long time, it has penetrated. You can't reach it just on the surface. So get rid of it.

Also check under the floors. If applicable, beams may be damp and the wood is rotting.