A few thoughts:
1.) Advanced OW cert. is required by some dive op.s for some of the dives. I've seen a couple of guys turned down for a wreck dive out of Key Largo for lack of it. Plan to get that.
2.) Nitrox is useful on high-frequency (e.g.: Bonaire shore diving, or live-aboard diving 4 - 5x's/day) or some moderately deep diving location where much of the dive is at depth (e.g.: Jupiter in Florida, off-shore wrecks of North Carolina, deep wreck diving). Plan to get that.
3.) Get some diving done. High-frequency diving is readily done on live-aboard (
Picking a Caribbean live-aboard) or shore diving Bonaire. Some land-based dive op.s offer 3 or 4 dives per day;
I had that with Rainbow Reef Dive Center out of Key Largo (4 dives/day); Little Cayman Beach Resort offers 3/day plus a little added charge night diving is there's enough interest IIRC. I've recently learned that 4 dives/day can be done in Cozumel, but apparently the destination doesn't lend itself to such as easily (
Aldora and 3P's reviews).
4.) Solo diving is great for some of us, some of the time. Not for everybody. How much experience you have to get ready for it I cannot know; I think the 'industry standard' of 100 dives is reasonable. By that time maybe you'll have had a few mishaps and a chance to see how you respond under pressure, and get a sense of how soberly you think through & conduct dives.
5.) Figure out your buddy philosophy. What I'm about to describe assumes popular dive tourist locales (e.g.: Bonaire, Belize, Cayman Islands, Key Largo) with benign tropical conditions (e.g.: warm water, good viz. (50 feet+), low currents (unless drift diving is the plan) and low likelihood of entanglement. Usually they are guide-led. Here are some buddy 'philosophies' that won't all be spoken, but will be practiced.
Type 1.) Nearby redundant air source buddy. You are likely part of a guide-led dive group, and you and your buddy occasionally look over to find each other, stay within several yards of each other (within allowable viz.), and if one of you has a problem (e.g.: low on gas), he can swim over to the other, signal, and get air, help, etc... But you don't expect anyone to notice you're in trouble.
Type 2.) Group Diver. Similar to Type 1, except since there's a sizable guide-led group, you don't depend on your buddy for navigation nor he on you, and in case of trouble there are a few other potential redundant air supplies in easy finning distance. You may not look for your buddy as much; if he's following the guide like you are, then he's nearby.
Type 3.) Tight Buddy. The pair discuss the plan in detail prior to splash, glance at each other frequently, note each other's general body language, are constantly aware within a small margin of where each other are, stay close and where they can see & be seen by each other and each is fairly likely to notice soon if one is narc.'d, faints, etc... Type 3 is most practical if you go on trips with a known tight buddy. 'I am my buddy's keeper.'
There are shades of gray (e.g.: advanced diver sort of shepherding a newbie, a photographer who's buddy does most of the buddy monitoring). Type 3 is what I think many on the forum believe should be the pervasive standard practice; Types 1 & 2 are what I think
really is the pervasive standard practice, but I haven't done a survey. Sooner or later it's what you're gonna get if you dive with a lot of instabuddies, though.
