Just be super careful with stone buildings. They function in a completely different way to standard buildings.
For your external walls, do not put stud and PIR in there. One thing to remember with stone buildings is they need to be vapour permeable.
If the walls cannot breathe, they will cause damp and mould issues behind. Because stone buildings didnt have proper foundations, damp will get into the walls (especially if internal floors are concrete)
Use something like wood fibre insulation instead, it will allow the heat to get to the stone and prevent a mushrooming in the gap
When I started taking off that stuff from my place, the first floor started to come down as it had rotted the timbers.