TBH that back end looks about normal for the mileage- it’s arduous under there! From what I see, nothing structural needs replacing, just stripping and painting/coating properly. Do the bushes and get it set up properly at the same time.
May I suggest you talk to one of the many specialists in Sevens? If you are down that way, I’d recommend PGM, or Ratrace. These “Blokes in sheds” are the true backbone of Caterham ownership, no flash showrooms or service departments, just pragmatic, good value advice and service….Just my thoughts.