[Quoth]

Now 6793 ebooks
16.6G or 32 G free.

Series, collections and subtitles are used.

So as some is used when there are no ebooks, likely the 32G Libra 2 can store 14,000 to 18,000 ebooks.

That's 38 years if you read one a day of 14,000.

Only a big screen with a PDF reference libraryand/or graphic novels or such needs more storage. All my documents adds to more than 200 G, but that's including 80 years of PDF service manuals, projects, CAE/CAD, research for writing etc.