What do you want to back up? Media and “linux isos” are usually huge and you cannot compress them further and not really worth it to fork out money for cloud. You can just download again or get 2 hdd and keep one disconnected.

If you absolutely want to go for cloud, i would recommend backblaze backup (the personal computer one with flat fee).

Stick your drives in the case to have them always connected to take advantage of backblaze (exclude the uncompleted torrents folder). And use whatever mobile rack you have to connect the backup drives.

Does it clock down when idle?

Obsidian, then do whatever you want with your markdown files.

That’s why you use 2 and have backup.

Keep the actual epubs and search in those? (You basically want a transcript of a read out book…which is the book itself.)