First, great choice on the boat! The 5800 is awesome!

We've never done a crewed charter with Moorings, but I would think you'd be able to choose where you want to go. Things can often change due to weather although we've rarely had to change plans significantly due to weather. As Twanger said, tipping is standard with a crewed charter. 10-20% as he said.

Regarding diving - the 58 is huge. Plenty of room to store tanks - they may even have a tank rack on it. Also keep in mind the 58's have full water sports gear - water skiing, wake boarding and I think tubing..etc. Plus paddle boards and kayak. If you are confident divers then I'd rent gear and have it on the boat and the crew can take you to some dive spots. If you are at all unsure or uneasy about it, then a rendezvous would be a better option. Our first trip we did a rendezvous and dove on our own right from the boat and it worked out well. Rendezvous was for the wreck of the rhone. We got the dive guide for the BVI and it was invaluable.

You'll have a great time! I'd highly recommend you take one of the cabins on the main level - it is cool to wake up and get a full view outside.