Hi Bob!
There is LXC and there is LXD. You are using LXC while my tutorial is for LXD.
The commands that look like lxc-xxxxxx (as in lxc-start) are LXC.
The commands that look like lxc xxxxxx (as in lxc launch ubuntu:18.04 c1) are LXD.
In my tutorial, I describe how to set up a profile in LXD that has all the GUI prerequisites.
Then, you can launch your new container specifying that profile, and the container is automatically a GUI container.
If you are going to stick with LXC, then you can try to interpret the commands from LXD to plain LXC.
I am not familiar with LXC and I cannot help you here.
I’ll be happy though to see such a tutorial for LXC, and it would be great if you could do the write-up.