I was moments away from putting this question on the forum when I spied the solution. I’ll post the question here in case it is useful to others:
When following “future Michael” talking more about nodes (starting around time mark 7:44), I made a new file as directed but my Nodes window was not like the one in the video. I had different nodes showing:
After fiddling with materials, alpha settings, trying to add the new nodes with Shift-A and getting a different menu, etc, finally I saw the new file was in Blender Render, not Cycles Render. Changing that gave me the right nodes to continue.
Cheers!