From what I remember I’m my time using Kavita, basically the only way it knows what anything is comes from the file structure. It’s called out pretty explicitly in the docs for example.

Now it’s been a year or so for me so maybe now there are options to define your own structure or pick from some but I don’t remember any.

I would recommend audiobookshelf for the audiobooks, especially if you have your stuff running in docker. It seemed to me like the solutions to force Plex or jellyfin to do books were a bit more hacky than I wanted.

No clue about specific deals but I’ll share a site that I found thanks to Lemmy that had some good deals when I upgraded to an 18tb HDD for $180 USD.

https://serverpartdeals.com/