I think DRM on Kobo books is dependent on what the publisher requests or something like that. The few I have bought don't have DRM from what I can tell.
I don't think you need a Google account to use Sandboxed Play Services in general. Maybe some specific things that require you to be logged into the Play Store but overall I can use Android Auto and other things I need without being logged in.
I've been using GrapheneOS on my phones since the Pixel 3 and I have not had this issue when using Verizon. For the other person maybe it was a different carrier? Or some issue a while ago with that carrier and GrapheneOS.
The problem I had with products like Airalo is that if you are traveling and need to actually call a hotel, excursion, or any company in the country you are visiting you cannot do that with just a data eSIM like Airalo.
Sure you could use WiFi calling maybe but in my experience when I really needed to call someone I had to switch back to my original carrier and incur the $10/day fee.
My problem with Symphony and other music apps like Auxio is that they don't work with audiobooks and file types like m4b. Simple Music Player worked for me when playing all my audio files but now I am waiting for the Fossify version to be published.
That's a good starter list. However it should be noted that all the Simple apps should be avoided now and instead people should use the forked versions from Fossify.
If it won't load because you try to block all their crap: https://archive.is/okwqR