I contacted support, but haven't heard yet - that's OK because it is the holiday weekend for working people!

In the mean time, I uninstalled Amazon Appstore from my Nexus tablet. Then I tried running iRealb and it wouldn't run because Amazon Appstore was not available. So I guess I must have Appstore on my tablet to run iRealb - since I bought it from the Appstore.

I am guessing that the solution is to buy iRealb from Google Play, and I would happily do that to end the Appstore problem. (The price is more than reasonable!).

The questions then become:

Do I uninstall-remove my current iRealb before purchasing it from GooglePlay? (Probably yes)
Do I perform a backup before uninstalling? (Definitely yes)
Can I then import my playlists (which include dozens of unique arrangements)?

Thanks again.