Yeah they will but you can pull them off once you are done listenning to them

since you're on lemmy, I'm gonna assume you're techy. Audiobookshelf can be self hosted, and can manage audiobooks and serve them.

It depends on how long the book is and how were audio files compressed. I'd put an average of 450MBs per book as I inspect my non-app direct downloads, with 6 Dune books being 2,5GB, more individual ones been from 250MBs to 1GB. If you reconvert them yourself, you can set the target bitrate => size to barely tolerable levels if you will, and keep in mind that's still hours upon hours of joy, they worth it, and for tough books you can download them in parts. Idk how tight your space budget is, but I found it's pretty nice that the whole Dark Tower cycle by Stephen King, being cleverly shrinked by the uploader, took only 6,5GBs while giving me a month-long ride.

Compared to most PDFs and EPUBs, audio is obviously a very bloated data source, but at the same time it provides a lot of advantages pure text can't.