.
In reference to my previous mention of adding squash files in Xubuntu
in item 3 above...

Canonical is introducing a new feature for adding programs to Linux systems
called snaps. This feature brings into being a whole new infrastructure
which is somewhat reminiscent of stacking compressed knoppix overlays.
Snaps, in effect stacks squashed file systems representing useful program
additions which bring their dependencies with them. By stacking, I mean
combining filesystems by means of a union filesystem. This infrastructure
includes a means of creating such snap packages, called spapcraft, and a
concept of 'stores' for obtaining useful snap packages or for offering some
packages you might create yourself for others to use.

Canonical introduced this system into Ubuntu, Debian and many of the more
popular Linux systems in 2016. It is contained in Xubuntu 16.10, for example.

You can get a feel for snaps with the following video:
https://www.youtube.com/watch?v=MCrT_AhCOYk

If you are interested in learning more about snaps, you might begin with
the following introduction and its references:
https://tutorials.ubuntu.com/tutoria...c-snap-usage#0