Damp, mortar and indecision

I recently bought a house that needs a bit of care. Some slipped slates, in need of decortating - no problem get some quotes for the exterior work and get cracking. Then I started reading about lime mortar and the semingly contradictary approaches of "DPC and waterproof sand and cement internal render" and "let it breathe with lime". And then I fell down the internet rabbit hole and am still no closer to reaching a conclusion.

The house was built in 1880ish of rough cut gritstone

The house

Currently problems are there are some damp problems coming through the plaster and some rotting joist ends and parts of the wall plates. First task was to unblock the gutters which has stopped water running down the outside walls.

Back of house

Front of house

Clearly this isn't the first time the inside walls have got damp as the top coat of plaster is cracking off just above where the render changes from a soft cream colour to a hard grey colour. So it looks like the bottom 50 cm at the front and 1.5m at the back have been hacked of and rerendered previously. There are white crystal salts on the surface of the plaster in the corner and the horizontal line at the front of the house stays damp even after days of warm weather.

Outside there is a concrete path all around the house a couple of centimetres below the internal floor level. Mostly this is angled away from the house but in some places water pools during heavy rain. The air bricks also seem to have been partially hidden.

Concrete path

Rear air brick

Front air brick, broken and covered with wire mesh

The pointing on the exterior seems at least partly to blame. In places there are holes between the stones where the soft mortar has fallen out. Much of the house has previously been repointed by smearing cement over the old mortar. Some of the cement mortar is stuck on hard, some is falling and some appears to be damaging the stone.

Soft, crumbly (original?) mortar

Cement pointing

Cement falling off leaving soft mortar

Stone damage

What to do?

So what to do? Obviously the roof needs repairing and the gutters coudl probably do with enlarging. I have had various quotes/suggestions for what else needs doin:

1. Cream DPC, repoint in 6:1:1 sand:lime:cement, apply clear waterproofer up to the eaves, hack of render inside and redo with sand+cement
2. Repoint with natural hydralic lime (NHL) 3.5, apply "breathable" lime based render to the inside

Lowering the path has also been suggested.

So is 6:1:1 mix bad for stone walls? Is cement the devils work? How much of the lime based method is based on visuals and conservation? Is it wise to spend the extra on lime? Do I need to hack off the internal plaster and how high?

Suggestions gratefully received. Opinions seem to be strongly held with little scientific testing to back them up so the more I read the less I seem to know...