I have 3 different libraries, one for comics, one for TTRPG books, and my main one for actual eBooks. My main library is over 4GB with over 1,000 books.
No, I haven’t read all of them, but I am working on it. They have been collected over the last 15 years from Sony eReader store, Kobo books, Amazon Kindle, B&N, Archive.org and other Public Domain books hosts, Humble Bundle, Story Bundle, and various other places.
Largest categories are Sci-Fi, Fantasy, and Mystery.
I wish there was a way to link to an Android app.
There’s a sync app for Android just noticed the other day on pstore - just getting into calibre so bit too early for me to be using it. Looks cool though.