For #2: You don't want to go mucking around with Calibre's library structure. Treat the library folder as a black box. Don't touch!
https://www.mobileread.com/forums/sh...d.php?t=119175
However, if you want to export the books back out, look at Preferences > Saving Books to Disk> Save Template.
This page explains the template language. GPM won't work.