Where do you put my 8,000 files on my kindle?

For the record, I’m a data hoarder. I also downloaded books illegally. I have one backup in my hard disk, but I’d like to have a second backup, stored in a cloud. I have an Amazon account with the kindle already registered. Do you suggest I put these files in there? I don’t care about the size or the time required, I’m just looking for help.