Hello, Kevin -- I'm always happy to meet a new reader, and a singing one at that. Yes, Caruso sang Lohengrin two or three times, a career misstep he backed away from rather quickly. Something like Melchior's few appearances as Otello when he switched from baritone to tenor. But a Heldentenor Caruso was not.
I stopped after the third opera book simply because the research was so time-consuming; it was interfering with that little thing called earning a living. I've always thought I'd like to go back and write three more, but it doesn't look as if that's going to happen. As to Mayra Montero's The Messenger -- alas, I've never heard of it.
So your first Rinuccio is this coming weekend? Kevin, I hope you'll come back and tell us how it went.