Booksonic developer here,
Booksonic should be compatible with any app that uses the Subsonic API, you will however loose out on book specific features like descriptions etc so I wouldn't really recommend it.
There is a fork of the Booksonic app available on the Play Store as well that's called Audiosonic but it hasn't been updated since june 2018 and is missing some critical fixes for newer versions of android so expect it to be a bit crashy.
With that said on to the Booksonic app, I totally agree with you that it can be quite unintuitive for new users and my main focus at the moment is fixing that so reading posts like yours is super helpful. I released a new beta earlier today and some of the changes in ít was after reading your comments
I purchased the Booksonic Android app (cost me $1 w/Google promotion). Setting up the network connection was frustrating ... and I'm only looking at LAN for now
One of the things addressed in the beta I released a few days ago is a better login screen so would love to know what it was you found frustrating about the setup so I can try and make it even better before release.
Several freezes, and too many "play" buttons, one of which seemingly takes me back to the beginning.
The freezes are a bit odd, that shouldn't happen, if it happens for you again please send me a log file and I'll see what might be the problem. As for the play buttons. There is no play button that takes you back to the beginning but if you select a track it will start to play that track from the beginning even if there is a bookmark available for the track, this will be fixed. You are right that there are to many play buttons and that they can be confusing, the new beta should make this a whole lot simpler.
No clear download option... although I suspect "permanent cache" is that... in contrast to "cache" which I assume loses the "permanent" feature.
Correct however in the new beta cache has been renamed to download and there is only one type (the none permanent one)
The way it worked before is that there was two types of cache, cache and permanent cache. In your settings menu you can set how much space the app is allowed to use for storing books. Then when you cache books it will fill up that space and when it reaches the set limit it will start to remove the oldest files to make room for new ones. Files that where permanently cached would never be automatically deleted this way.
I tried bookmaking, but can't find my bookmarks.
Your bookmarks are available in the drawer (left menu) but you need to enable that in the drawer menu under settings. In the new beta this has been changed so it is enabled by default.