Probably depends. There are some services which I know are rock solid and have never failed me when auto-updating in 2+ years now.
However you are right that it can cause issues. I forgot to mention monitoring totally. My bad. A service like uptime kuma is really worth having for that reason. For a few services that really saved me a few times tbh. I set it up to broadcast status changes to a telegram channel and a special mail inbox. But it can seemingly use any and all services under the sun.
If you only have a handful of services, manual updating is good for learning and can prevent problems by seeing them immediately. However once you have so many services that you can’t possibly update them all or have the motivation to, it’s better to let them auto-update and have a service like uptime kuma notifiy you if something goes wrong imo.
As with all things in the world, it’s matter of striking the right balance of tradeoffs.
If you’re mainly gonna read pdfs, an ereader is probably too small to use comfortably.
Look into eink note taking devices instead. They’re basically similar to a kindle, but also usually have a wacom layer to use their pens to annotate pdfs. Also they’re usually bigger (at least letter format) which makes them way better for that stuff. Most support epubs too.
I used a reMarkable for some time. It has a cool homebrew community, since the creators are pretty open and just give you the root password. They also have their own sync apps and subscribtion stuff if you prefer that.
At least Sony and Boox have some similar devices. Some come with Android which might be handy for you.