Farmhouse Development

I’m currently looking at developing a 19th Century farmhouse into a modern dwelling. Currently the rear and side walls are heavily buttressed and the front wall warps out about 60cm from the centre line in plan. If I wanted to keep the original stone walls, and re-roof, dry-line, re-floor etc. the interior is there any way of assessing the structural integrity of the existing rubble stone walls? Another thing I was curious about was the addition of a concrete collar to act as a levelling wall plate for any new roof which I would be adding. Isnt it a bit dodgy adding concrete elements to a lime mortar building? What are my options here? Structural steel frame inside the skin?

I know that the most practical thing would be to knock the whole lot and build a decent modern building over it but I’d still like to keep the original facade and couldnt bring myself to erect a faux-farmhouse exterior to a modern house.

Any and all advice would be greatly appreciated.