I don't own a dive shop. I have two very close friends that own two different shops. I occasionally manage one, and I help out a lot at the other.
I can't think of any place I've ever been to that had more competition than the Keys. There's no way in hell I'd ever open a shop there. Just drive through Key Largo and see how 3 out of 5 dive shops are out of business. Do you think you can offer something they couldn't?
The start up costs are enormous. To get a serious product line like Scubapro, Halcyon, Oceanic, etc. you are looking at a huge investment. I think our initial order with Oceanic 20'ish years ago was in the neighborhood of 30k. Yes, I know you can get with Cressi or Sherwood for 8k or less. But you have to be able to stock the shop. You are never going to be competitive with price if you are buying gear one piece at a time as a customer comes in and orders it. Also, customers want to walk in and walk out with the gear. If they have to wait for the gear, they might as well order online, save on tax, and get it just as fast. We have over 100k in inventory at all times.
On top of that, you need a compressor. Bottom of the barrel, used compressor, 5k+. You want something decent that you won't have to worry about for a few years? 10k+
Are you going to bank nitrox? Are you going to bank Trimix? Money money money.
Do you have the necessary education? You need to be able to teach everything. Which means you have to be certified in just about everything. Are you technical in nature? Can you do rebuilds on regs? Are you certed to rebuild any regs? Or do you plan on paying someone else to do that? There's another expense.
I've owned several businesses. I've never had any business that required as much start-up money and time and effort to maintain as a dive shop. It's doable, but I'd rather not risk that much money, give up that much time and energy, for something that for many people kills the passion of diving for them.
If you're not willing to be the best, and offer everything and more than your competitor, don't even bother. You'll be broke in less than 2 years.
PM or Call me if you want to talk more. My phone number is on my website below.