No limit on the number or space of uploads per person, each individual file upload is limited to 25mb.
So far about 22,000 books have been uploaded, taking up about 12gb. So about 500k/book average - note I store extracted cover art alongside the books, so that pushes the average size calculation up a little. Storage shouldn't be an issue, it's hosted on
AWS , so storage is cheap (and can be increased on demand)
