You may want to do some checking before you head off in the divemaster direction, it may not be for you.
The Massachusetts shop where I took my courses wanted me to sign a bleedin' oath of alegiance, actually a non-compete agreement. In return I could get free air. Then there was the insurance and liability issue. No Thanks, not for me. After I finished my first First-Aid course I was told that it should be renewed about every two years or so. Ok. After about two years I asked about another class. They told me if I could round up enough people we could have the class, they would charge us of course. Me do the organizing, they take the money. And what's with the 2500# fills? I bought all my original gear there and I'm sorry I did. I go to a local Rhode Island dive shop now. What a difference. Wicked nice to deal with. The way it should be.
Besides all the plan your dive and dive your plan, sword, and all the other vitally important basic open water education, here are a few thoughts...
Don't get hooked up with a shop that doesn't treat you right the first time.
3000# cylinders should be 3000# in the water, even if they're rentals.
Rent at first, then IF YOU DECIDE TO STAY WITH IT...
Buy top shelf gear, every time you use it you will be happy. A weight integrated BCD is very nice, or get the suspender style weight belt, they save your back. Definitely get a computer, I use a Suunto Eon. Not cheap but worth it. You can download your dives and plot them out to keep with your log book. Diving is pretty expensive if you buy the gear.
If you try to buy life insurance and tell them you are a diver you better be sitting down when they give you the rates. If you need medical assistance, because of a diving accident, some of it may not be covered by your health insurance policy. These things should be discussed during your open water classes. If not, you should ask.
I feel sorry for those that don't live near the ocean. Fresh water diving leaves a lot to be desired. The ocean is just teeming with life. I go mostly to Cape Ann in Massachusetts, sometimes to Newport or Jamestown, RI, the vis is decent most of the time, usually 20' but never 50', (sometimes 5' and that is what we call a plankton dive). Plenty of lobster, flounder, crabs etc. My brother is a Massachussets resident and has the non-commercial lobster diver license, I have the Rhode Island version.
I don't know what it is like to dive in warm water, if I went it would likely be the end of diving around here for me.
I like night diving a lot, there is a complete change in the creatures that come around. Some are eforvescent in the dive lights. Some, like schools of squid, are ghostly transparent. If you sit on the bottom and turn all the lights off you can see what a different place the sea really is. The only bad thing about night diving is the mosquitoes if you do a shore dive.
We often rent a seat on a dive boat. $55.- for half a day, boat only, your gear and your air. Usually two dive sites. Boat diving is very nice. No sand in the gear. One giant stride and there you are in 100' of water. Yeooow.
There are many many shops near the ocean that will arrange a buddy and/or a guided shore/boat dive for visitors if you give them a little notice. This is a great way to go diving while on a seaside vacation.
Diving is good clean fun. You meet a whole different class of people. Most of them are real nice (not me and not my brother). On the dive boat there are women sometimes and it get's interesting. You'll see.
One thing to keep in mind when you go to the Carribean or somewhere similar is you need to gas off on the last day of the visit to avoid problems flying home. So, no diving on the last day, it is reserved for drinking. And yes, you can vomit through the second stage regulator and survive.
I like diving a lot but it interferes with my drinking.
My wife says she will leave me if I don't give up diving. Gee I'm gonna miss her.
And when someone asks "how deep do you go?" the answer is "all the way to the bottom".
Drysuits and the "P-factor" are not compatible.
All kidding aside, I have PADI Rescue Diver cert. I think this is a good cert level for the recreational diver. Enough useful info to be safe without making a career out of it. I really enjoy diving, I'm very glad I was talked into it.
All the best,
Martin