If you delete them, new cache files will be created next time you launch the application.
You could drag all the images to an external hard drive (using Organizer - not the operating system) but the cache files and catlog are best kept in the system files.
I Have at least 10 copies of each file! Is there anything I can do to search for the oldest files and delete them, keeping the newest cache files?
Strange. Do you have several catalogs or just one?
What is the difference in naming of say all 10 "thumbs.5.cache" files? Are they present together in your catalog folder?
Is this a converted catalog?