Re: 30" stone walls - opinions on insulating on interior
I think we're underestimating the thermal mass. IF you have enough thermal mass, you only need to be concerned with average daily temperatures. So in winter that means you can size a HVAC system in WI similar to one in Seattle. A northern home with stone won't need AC< just a whole house dehumidifier with ventilation.
However, even insulating it form the inside you'll still have the similar affect of the thermal mass because if you for example add 3" of spray foam between 2x4's, you get an R-value of 15-18, but the delta T will be based more on the average daily temperature plus any solar heat gain. The BTU's gained or lost are based on the stone temperature and divided by the R value of the foam.
I get some of this sme effect even with just stucco walls and plaster inside my house. I basically have 1" of light concrete providing thermal mass wiht two 1/2" pieces of beadboard for insulation. People are shocked at how low my ulity bills are for a oild house this size.
What you don't want is air movement between the insulation and the stone. You will get condensation and mold... guaranteed. Either keep it sealed or let it breathe. That's why spray foam is the best choice IMO.
1925 Two-Story Stucco Beaux Arts Neoclassical