There is already documentation for the Instant Games plugin here, which also links to Facebook's official documentation for guides on things like testing and publishing. I also added a note to the top of the Facebook plugin documentation saying it's not compatible with Instant Games.
Thank you! That note helps.
There's still lots more that's unclear to me. It feels like answers are scattered among Scirra docs, Facebook docs, Scirra forums, other forums, some of which conflict with each other.
So, I still wish for a tutorial written by someone who just got their first instant game working. As a newbie, I learn best from someone who just did what I'm doing. They know what isn't clear from existing docs (experts are too immersed to realize what newbies do and don't see!).
(And, who will write this well? I still think Scirra would be wise to reward anyone who writes a good tutorial on a key topic. It's a lot of work, and steals time from making games...)