Everything is in books.db isn't it?
author is in books table, column name is author
tags / series really only applies calibre anyway right? Collections are only supported in built in reader app. collection is master table with names and ids, and there is collections table which is one to many with books (also has sort order)
I think if you want to support any way to manage books in your homescreen, you would have to go with the SQLite databases and/or scan each epub yourself and create a metadata cache similar to what calibre does. If you want to provide a "calibre enhanced" homescreen only then yes everything you can get from the calibre metadata cache on the device.
In anycase good luck with your project no mater what you decide to do!
