I am about to start mine. If the interior walls are solid, I would leave them as-is.
Mine look not-solid, I think the honeycomb core has deteriorated in many areas,
in which case I think better to strip it off and replace the core with insulated foam and a new interior skin, probably wood panels because everyone loves wood wood wood.
I may remove all the windows and redo it as solid wall and put in windows afterwards were wanted.
Would like to hear from someone who has done it..