Sorry, but you have it backwards and should be asking in MOON+ on how to make it work with Calibre the way you want.
Think I am wrong?
Open the WEB Browser on your PC and sign into the content server. Click search. (see image). Those are what I can use to find books (NOTE that even Calibre's 'Saved Searches' is available. There was no need to bastardize (organizational trickery) the data entered in Calibre, just write that magic search and save it for use on a remote device. If your device can't use that...it is a devices limitation, not Calibre. (FWIW The metadata plugboard is a feature to use to trick devices into doing things the designers left out, while leaving the Library data pristine and usable by less limited devices
. But the plugboard is only for SendTo type actions)
Calibre is a database.
You should not have to 'organize' it to access and use it.
It is Organized in a manner that allows books to be found by many criteria (the most common being: Title, Author, Series . but that is not the limit.) All the rest are things you supply the MDE (someway) upon adding the book are allowed.
FWIW I mostly used Moon+ with Calibre Companion (Back when it was good) as an alternate way of seeing my edits on a device NOT my EZReader OR as lenient as a Web Browser based (includes Calibre Viewer) . FWIW every device has its foibles. Calibre is too easy going. Older ADE finekey. Kindles (old mobi) just limited (no CSS). The real book wranglers out there lost a lot of hair trying to make books work on a wide range of devices without multiple
device dependent releases (a maintenance nightmare)