1) Plenty of storage - I wouldn't keep the gear in the bag, but I'd store it in the bow storage area. Rental tanks can be stored in a rack along the side or stern.

2) Not at all. For starters, he really shouldn't be diving alone. If I was the Captain, I wouldn't allow it. I'd insist on him not diving or doing rendezvous dives only. Only issue with the rendezvous is it takes time as its a two tank dive. Pickup is often around 9am and drop off at 1pm. One time we didn't get back until 3 due to a boat issue.

We always dive, so its never an issue with us, but I'm a diver so that helps. But when doing it from the boat (which again, I wouldn't advise since he'd be solo) its easy to do at a snorkel stop as many dive sites are great for snorkeling. While the rendezvous takes more time, that can be worked out as well as the pickup and drop off spots could be different or the rendezvous could be done from a spot where you might spend more time.

Ideally spend two nights at Leverick. Arrive on a Thursday and you can rent a car and go out to eat at Coco Maya or Chez Bamboo and then Friday explore the island which he goes off diving with Dive BVI (right there at Leverick) and then Friday night you've got the BBQ. This way no one is holding anyone else up.