"I understand that the SVIs are the best kept secret in the sailing world"

This is a quite the stretch. SVI is nothing like BVI in any way and will never be a BVI. I would call SVI cute, inexpensive, not crowded, and very nice. I would buy this cruising guide, very informative https://www.amazon.com/Cruising-Guide-Pu...VMP89AK7FGNJ7HZ
I would check out CYOA for your charter.