Du kannst den F-Droid Store installieren (apk per microSD installieren). Darüber bekommst du einen aktuellen Firefox (ohne DRM, nennt sich Fennec), sowie diverse Apps zum öffnen von PDF/E-Books.
Und mit einem modernen Browser kannst du das Gerät auch als 2. Bildschirm verwenden, Deskreen ist da dein Freund.
is is bad, but usable. when i have to do colour sensitive work i attach my ipad or iPhone with me (which i always have in hand) and use it as a second screen or stream my pc screen to it via deskreen
I tried getting this working with Deskreen (https://deskreen.com/lang-en) but just got a black screen with a cursor. This is probably because Deskreeen recently uses an old version of elector I'll see if forking the project and updating the electron version fixes the issues.
There is so much in that link to cover. As a note, all that cool syncing comes at a price, you are locked into a paywall system. I will let you digest that horror-fest as you will.
SMS: You can sync SMS messages two ways; Gsconnect (GTK) / KDE Connect (QT), or Android Messages has their own sync app which is not as clunky as KDE Connect. You can find it in your repos, AUR, flatpack, etc.
Text/Link Copy: You can copy test, links, etc from one device to the other via KDE Connect.
Tablet as second screen: There is one app I know, but there is probably more. Deskreen which is in AUR if you are on Arch, probably elsewhere via repos or build from their website.
File Sharing/Remote Mouse Control/Keyboard: again all with KDE Connect.
I haven't tested it but I think https://deskreen.com/lang-en could work.
Screen mirroring should work out of the box, for real extended desktop usage you need a dummy plug you could buy on amazon for the cheap or tinker with the os to make it think it has another screen atached. But just for testing it's not needed.
I've never done this but one disadvantage is you're limited to a laptop, not a desktop. This will make it harder to have a multimonitor setup. There is some software you can use to turn tablets and other devices into a second monitor. https://deskreen.com/
Make sure to have a backup computer if you're living remote places where you can't get buy a new one easily. You really don't want to miss a deadline because your computer breaks and it takes a week to fix/replace it.
If you do this, it would be cool if you kept a blog with some updates on how it goes.