You dont have to chage the disks if they are in good condition, have a look on
www.fubarnet.com there is a guide there.
Can I just buy the rubber spider without having to buy the steel mount? (Rear exhaust mount)
No you have to buy the whole thing, its about £20 from renault, dont replace this alone, replace the middle mount aswell. I can supply part numbers if required.
Is it easy to replace?
Very easy its held on with 3 bolts.
Is there a nut on the exhaust rod that attaches into the mount?
Yes, 8mm iirc, it should be easy to undo theres one on the middle mount aswel.