I have changed the seat bottom cushion and just the cover several times on different seats. Actually pass. seats get less wear so the foam is usually in better shape than the driver's side, so changing the whole bottom is best IMO. It's actually pretty easy and may be possible without taking the seat out. Two half-clips, bend the steel bar, release two springs. But if you're going to do the seat back then taking the seat out is necessary.
Changing the seat back fabric is something I am going to do, the same as you, using the fabric off a pass. seat and new hole/ plug the old hole. I may take that part to a shop though and have them sew a patch, using fabric from the material that gets taken off. My understanding is that this is the only difference, there are no other 'gotcha's'. You might want to replace the lumbar support while you're in there.