I'm happy you are planning to learn to dive! The world needs more divers.
I don't know anyone who as done the online classes, however PADI
both offer them; there may be other agencies that do but those are the 2 biggies AFAIK. Instructors may be either one or the other but not both, so choose your class/instructor combination accordingly. As an aside, I will say that the PADI Advanced Diving course book
was excellent. PADI has made an effort to employ educators and seems to have worked hard to improve the user experience.
From the web site:
Prior to certification as a PADI Open Water Diver, you'll visit your PADI Dive Center or Resort to complete your training. You'll take a short eLearning Quick Review to confirm your understanding of safety-related material from the course, and you must successfully complete five confined water dives and four open water training dives with your PADI Instructor. You learn and master each of the required skills in confined water (swimming pool-like conditions) first before moving on and showing your instructor that you can comfortably repeat those skills in open water. As a PADI Open Water Diver, you will be a certified entry-level diver able to rent dive gear, get air fills and dive anywhere in the world in better or similar conditions to those you've trained in.
NAUI's web site isn't as informative but it's safe to assume the in-water requirements will be similar.
I'll state the obvious and say that you'll be doing around 9 dives with an instructor, so it's best to find one you're comfortable with. How important is that? It depends. If you think you'll have difficulty with any of the in-water skills, connection with/trust in your instructor can make the difference
between success or failure to get certified. For this reason, you may want to choose an instructor before paying for any particular online course.
One great and unique thing about Florida is that there are fresh-water springs that make great places for some of your training dives.
I didn't really answer your questions, but I'm pretty impatient for diving weather and in a mood to think about diving at the moment. OJ, people dive for many different reasons. What is yours? Do you have a ready-made dive buddy and a group to dive with? Will you dive for pleasure or work? What do you hope to get out of diving? You may get more info if you can share your vision a bit. Then again, there aren't many other divers here and aw heck I'm just nosey!