If you're just looking for ebooks Calibre/Calibre-Web will do the job. I wanted a good audiobook player too so I went with Audiobookshelf as it does that and a few other things. You could also go with Jellyfin as I've read it can do epub, but I have no experience with it.
I highly recommend AudioBookShelf . It's mostly geared towards audiobooks/podcasts, but it has a decent reader built into it. That being said, it's not without it's flaws, like some document file types aren't recognized, and not properly syncing progress occasionally.
Edit: I should mention it's actively being developed, devs are active on discord & GitHub, and it's getting better all the time.
AudioBookShelf is awesome for audiobooks. I can't speak to its capability as an eReader but I thought I'd throw that out there for anyone wanting a second opinion. I use it daily and the Android app is great too. My go-to audiobook server for life if it stays just like it is right now.
I just set up audiobookshelf yesterday for audiobooks and podcasts. I tried out the e-reader, and it's not good enough for real use. It doesn't save your page, and it's super barebones.
As an audiobook server/app it's fabulous, so I'll be sticking with it for sure. For podcasts, it's pretty great, too, but missing a few features like badges for unplayed episodes, and an "up next" queue/playlist that gets auto populated. I switched to it from pocketcasts and the downsides are things I can live with, but I'm excited for when those features are added.
For an e-reader, I'm going to set up Calibre and Calibre-web, while keeping an eye on Readarr development.
For general 'non-book' type documents, I've also set up a Paperless-NGX instance. It's working fairly well, but I'm still in the learning curve phase of getting it set up exactly how I want it.
With Audiobookshelf you need to download the Podcast episodes to your server, right? You can't just subscribe and stream them? That's what has kept me from using it for that. I would like to get away from Pocket Casts as well.
That's right. I don't know if you can just stream an audio file from an rss feed without downloading it first?
The thing that frustrates me about audiobookshelf for audiobooks right now is actually the opposite problem. I like to have my podcasts played locally from my end device (for when I'm on the subway or in the woods and don't have signal). I can download podcast episodes from my server to my phone, but if I'm playing a playlist, it streams from the server instead of playing local copies (looks like it will be fixed soon https://github.com/advplyr/audiobookshelf-app/issues/734), and there is no way to automatically download new episodes to the app when they are added on the server when on wifi (looks like there are no plans to add this feature https://github.com/advplyr/audiobookshelf-app/issues/680).