Been to Norman on a sailboat, so I don't know what the public transportation deal is from Tortola. Norman is indeed the Island that inspired Treasure Island, and it's a fairly easy hike up to the top of the hill that overlooks both harbors. Rereading the book before you go helps! The remains of a fort or two that would certainly have been inspirational are also easy to discover and explore. It is a very evocative place.
The caves are unbvelievable. We went into several at night in a Zodiac with a guy who knew them well, and who also knew how to tell a pretty good ghost story. Just a flashlight or two, and a couple bottles of champagne. Again, I don't know whether there are trips available to the caves on a per-person basis, but if there are I would highly recommend them.
It's a fascinating, largely undiscovered Island, and the Treasure Island angle really sparks the imagination.