I'll answer a few..

1. I'd start with a week. Think space, how long it lasts..etc. Using a provisioning service is fine. You can easily re-provision in a few spots on Tortola and Virgin Gorda.

2. You shouldn't anchor in a mooring field. The cruising guides and other charts do show areas where you can anchor.

3. Plenty of places to fill up on water all around. I don't recall the cost off hand.

4. Visit LIME or Digicell and get what you need direct from them.

6. Prior to Moorings doing this themselves, we used last stop and were happy with them.

Sounds like a fun time!