Live desktop and DocSurf
I am not going to use Caja, but Nemo over Nautilus, so can’t help much with using Caja.
I did that in both Ubuntu Unity and default Ubuntu, but simply can’t remember how today. Best you should invest your energies to create the live iso with 19.04 than 18.10. Ubuntu had linked some folders in root to /usr, just like it was done in Arch long time ago. And, also 18.10 is practically dead.
Hope you’d read the thread testing-unity-session-in-19-04 from the beginning, you would see what we have been experimenting on. You can also build with the mini iso on UEFI.