Did not search the entire thread, but a good source of free Science Fiction/Fantasy ebooks is Baen Books' Free Library. They are published in multiple formats without DRM.
https://www.baen.com/allbooks/category/index/id/2012
In addition, a number years ago Baen used to include a CD in the back cover of their hard cover books that had previous works of that author and others. That is how I got a start on my collection I manage with Caliber. Probably worth checking for hard cover Baen books in second hand book stores