Busy at work, so progress has been slower than I’d like. A few comments on Chapter 6 for others who may come along:
For setting up Ubuntu Mate 18.04 (p175), bullet #2 - you really should set up the user as “pi”. I chose a different username only to discover that the scripts run further on (p180) expect the “pi” user and won’t run otherwise.
For x11vnc - Forcing the HDMI output - there is a note in /boot/config.txt strongly asserting that you shouldn’t edit the file, and there was really nothing to uncomment. Instead as suggested I created a file /boot/usercfg.txt. That worked fine (mostly). As long as I’m connected to a monitor, I get a good display. But once it’s headless, my display is only 656x416, which I’m afraid will be nearly useless. After an entire afternoon of googling and trying different things (including assigning framebuffer width and height), nothing works. Any suggestions would be welcome. I’m going to try this. If it’s unworkable I may try tightVNC. Or I may just load a non-GUI version of raspbian and try that (I’m guessing that’s where I’ll end up in the end, but have wanted to follow the tutorials as is as much as possible).