First on the list is to insulate the attic with at least 30cm of good quality insulation, and if the party walls do not go all the way up to the ridge, then construct a fire retardant wall to divide your attic from that of the neighbour’s.
For the walls, changing the exterior appearance needs planning permission which is a pain in the neck, and is often subject to the personal whims of local officials.
Insulating the inside is much cheaper, far less hassle, and easily within the capabilities of most folk who can use basic tools.
Polystyrene panels glued directly to the existing (sound) surface work well. Plasterboard is available with the polystyrene already glued onto the back, and a sheet of 10mm board with 40mm polystyrene glued thereon is actually lighter to handle than a standard sheet of 13mm thick board.
I used a base layer of just plain polystyrene panels first. They come in different thicknesses, so by using combinations it was easy to make the walls vertical.
This also allowed the easy cutting of channels for pipes and cables to be hidden behind the final surface. The final layer had the joints offset to the under layer in order to create a completely waterproof surface. Fill and sand the joints, and then direct decoration onto the board surface preceded by a couple of coats of sealer to keep paint costs down. (I make my own sealer from the cheapest white emulsion I can find with some PVA adhesive added.)
For the ground floors, if there is sufficient headroom available, I would basically construct a wooden stud partition frame laid across the floor on top of a continuous damp proof membrane (plastic sheeting). Drill through the frame for whatever pipes and cables are needed and then fill the spaces in the frame with insulation, then OSB board onto the frame, and then the final surface to your preference. I found that laminate flooring onto a 3mm cushioning layer works really well for various reasons.
It will of course be necessary to adjust the doors to accommodate the raised floor level.
With appropriate planning you will be able to cover and hide all the cables and pipework as the insulating process proceeds.
What you will end up with is an insulated box within the pre-existing structure that has smooth, clean, sound, vertical, and flat surfaces that make installing cupboards and fitted wardrobes so much easier.
Good idea to insulate the party walls as well. Not only will it reduce damp and noise transmission, but an empty house next door can rapidly end up being markedly colder inside than the air outside in the street.
The question of insulating between the living rooms and the bedrooms on the upper floor is more a matter of reducing sound transmission than anything else. You may wish to consider the inconveniences of the sound of the TV rising up into the bedrooms, or indeed the noise of other activities permeating downwards. It’s a question that is greatly affected by who is going to be living there.
Complete insulation will of course substantially change the appearance of the interior of the building. I know some folks who just love the look of the old stone, but then they have deep pockets that can afford the heating and dehumidifying costs that go with that medieval look.
Personally, I like clean, dry, warm, straight, and cheap to run.