The Library folder is THE LIBRARY. (you should never do any changes inside this folder EXCEPT Copy it in its entirety) I contains The DB, Books and covers. It also contains files to allow
rebuilding a damaged database fairly quickly. (do not use ADD Books to rebuild...Last resort)
The original source for the books is just an archive (if wanted.) and can be moved or tossed .
Calibre has included a tool to backup a USERS settings and Libraries (yes, it will include those if they show in the Library icon) and User plugins and settings
Click the Library Icon Export/Import all Library data (this is where a previous Export is Imported) <you need a large drive that can hold all these at once (not the same flash as the Library is on)
Get a portable HD or SSD, Flash is very slow and will take hours (or more) for a typical MR users Library.