Fresh install - everything seems to have gone well. Installed in stages as described by Dave Hamby. Roon sees new audio zone, but Pi display says zone not found. Extension enabled. Digione chosen in setup. Rebooted and repoweered a number of times.
Typically this is due to the Roon Control Zone not being typed exactly the same in the Display tab as it is defined in Roon Settings: try copy and paste to be sure?
That was the problem - missed a step in naming Roon Control Zone - much appreciated!
It looks great, and will soon sound great.