Automatic updates, they install Software as Flatpaks, GNOME is good for Tablets.
As the RAM is very low, maybe regular Fedora Workstation though. Or you layer all the Packages as RPMs, which is also totally possible.
Depends entirely on how many things these tablets should do.
webbrowser: Brave or Firefox
drm video: available in both
social media: easy as webapps with chromium/brave
youtube: freetube
signal, other messengers: flatpak best
In general Flatpak apps are often working better, on Ubuntu and Fedora base for me. Arch may be something different, but no way unless its controlled like on steamOS. Immutable Arch with tested updates would be great.