On a machine with 2 GB of RAM, what is going to make the biggest difference is using a 32 bit distro. Everything, not just the desktop environment but also all the apps, is going to take about half as much RAM. At 2 GB, that takes your system from functionally useless to quite useful ( especially if you plan to open a web browser ).
There is an option you did not list that impressed me recently. Trinity is a desktop environment that is essentially modern KDE 3.
The 32!bit edition of Q4OS makes it easy to install Trinity. It is basically Debian under the hood so you get access to all those packages ( at least the ones available on 32 but ).
Other than his choice of video player not supporting Wayland yet, why is this perfect for X11?
If he is only going to run one app, he can use Cage.
https://github.com/cage-kiosk/cage