Seconding Bookstack. I’ve embedded videos in it and I don’t recall anything special to do it. I also think there’s a way to comment on specific pages…mostly because I remember disabling that functionality.
Agreed on the roles and permissions aspect though. It’s pretty standard to do that for bigger deployments, but it may be a bit overkill for a single user instance.
I run calibre off my desktop. You can enable the Calibre content server and it can serve up your books for download (or provide a web reader).
If you have an Android device, you can use something like Moon Reader (or any other reading app that supports epub or Pdf) to download content from the Calibre content server.
With respect to covers and metadata, Calibre can tag and fill in this info as well - out of the box it will scrape information from Amazon.
I’ve used this since 2015 or so. It runs well on limited resources (we have it on a $10 / month VPS), and is pretty straightforward to use and even extend.
The opensource version is great and fully functional. We have bought the extended reporting and bpm pack which was also well worth it. Honestly, I can’t say enough nice things about it.
I believe in evolutionary biology circles, they call that the great mistake. But hey, you get none of the calories and twice the taste :) /s