Update (shamefaced!)
I’m posting this here on the offchance that someone else having troubles displaying a slideshow can get benefit from it – I’ve (finally) resolved this part of my question. In the Path to the Imagerotator (URL):
field I had https://MYDOMAIN.com/wp-content/uploads/imagerotator.swf
which had automatically been filled in when I hit the Search Now button to locate it. By changing the https://MYDOMA...
to https://<strong>www</strong>.MYDOMA...
my slideshow magically appeared. Yay, one down, one to go. Now, just to work out how to link individual images to pages rather than larger versions…