Hi Will,
Long Island is one of my favorite places on earth, but you have to know how to take it. There is very little tourist development except on the north end, and that is low key. Most of the population are farmers or commercial fishermen diving for lobster and fish. You will need a vehicle. Car rentals are available, but a little rough by first world standards. Boat rental businesses don't exist. If a local trusts you, his boat might be had. Its probably his livelyhood so they can be a little reluctant. One unfortunate thing, the Bahamas are expensive in US dollars, everything you consume will cost double stateside prices. Rentals vary from very pricy to acceptable.
The best way to do Long Island is get friendly with the natives. There are lots of very good divers there, especially around Salt Pond, and they will be interested in what you're doing. The locals are fantastic people, but the culture takes some understanding. Bahamians don't like to tell you no. Often, yes really means no. You can't push'em. This, the slow pace of life, and limited local resources can make you crazy, if you need something and time is short. Careful planning helps a lot.
The ocean diving is outstanding, but access is tricky. Get someone to take you to Millers, the best structure is just south of the tiny harbor. You can dive the reefs from shore, but that involves a pretty good swim in Very sharky water. I don't reccommend it. For some reason, the reef sharks there can be aggressive as heck. Unless you are in Clarencetown, which has a big harbor, a small skiff in the back of a pickup launched off the beach is by far the best way to handle it. Some of the reefs off Stella Maris (northern end) have suffered much in recent years, I'm not sure about Millers or Clarencetown. Diving out of and just north of Clarencetown used to be fabulous, , 30 meter plus vis(40 m at times), big ledges, sharks sleeping in caves. Acres of huge staghorn in 50-60 ft of water, unbelievable. I hope it is still like that.
I've not dove that blue hole and can't remember if it is closer to Clarencetown or Salt Pond. Clarencetown has some houses for rent, probably not much in Salt Pond. From the description on the above website, it must be closer to Clarencetown, near the end of a section of coast that is sheltered from the southeast trade winds. That should be real good for ocean diving conditions.
Keep me posted on your plans.
Connor