Thank you, David! You're awesome and the great Calibre is magical. I made a test sample, an epub catalogue of 200 books. The epub file is only 1.2 MB with all kinds of information in it. It's also editable in every way, I can strip it down to a tiny size. Wow. No more worries that whatever list making app or book cataloguing app won't be able to handle thousands of titles or that it'll take up too much space.
Thank you and have a nice weekend!