LTT - the red chair is a two tone pigment not a rub off. The top coat is a dark maroon not black, and took Remover 3 / Leather Prep and agitation to cause colour to come off. In my experience, alcohol cleaner is sufficient to get rub off black top coat moving in most cases.
Derek, I bet if you look at the green sofa with a microscope on the back / sides there are no hair follicle holes showing like there would be on a micropigment or aniline, and I bet it doesnt absorb moisture on the undamaged areas either. Two tone pigment.
The damaged panel will need a good grain pattern match to the adjacent panels - often difficult as the grain pattern has probably worn away in the damaged areas. A fairly flat replacement panel with a soft "hand" to mimic the softness of the damage on the adjacent panels may be best. But as I said earlier, colour is not important as you will repigment it to match the rest. Any old bit of leather will not do as it would stand out a mile if a poor match.
£600 to £700 is a good price to do this sofa - the client may have paid 3 to 5 times this originally, (although I doubt it from the pictures!) but make sure if there are matching chairs the client will accept shade / pattern differences between the restored piece and the rest, as you will never get it perfect. I prefer to do all the pieces of a suite if possible, as then I know they WILL all match at the end!
Good luck with ther survey