Again my advice is put some more dives under your belt before you take the AOW,
1) You will do more dives less homework
2) You will improve your skills by diving
Sometimes when you are in a site like that the instructors try to rush the class in order to get you done with fast and get you to dive ASAP, is too much info all at once, half of your vacation you will be reading the book and your day will be wasted, i mean bo wasted, but why to spend all that time in a class when you can be diving or on the beach or in Tulum, Chichen-Itza, etc.. is so many things to do down there, on your own pace.
Book as many dives as you can, go to the cenotes, avoid the wrecks, too deep and strong currents, i'm sure you will be able to handle the dive, but the question is, "are you going to enjoy the dive?" maybe not as much as if you do some easy shallow dives, all dives in that area are challenging, for the most part you'll be doing drift dives out in the ocean, so i'm sure all this is going to help you to improve and learn new skills.
about your buoyancy well that is something that is going to take some time and practice, but is very important you keep control of that too, first and most important for your own safety, second is because if your are landing over the coral you may kill it and as a diver and embassador of the seas up here in land you do not want to do that, but i'm sure your guide, most of them to the level instructor or at least dive master can help you with that. My own advice is when you get on the bottom take your time do not rush in to the dive do a gear check get confortable with your gear make sure everything is fine then get your buoyancy in control try to position yourself at 5' above the bottom, you want to keep your head looking down, this way your neck won't get tired as fast, by keeping this distance your field of view will be wider, you won't step in anything and you won't disturb the bottom, dive slow, remember is not a race, very important use an operator with small groups, the big operators rush you during the dive they go so fast with so many people than you hardlly see stuff.
Well if you have any questions feel free to PM me, i do not know many operators in playa, but i know Manta divers and Scuba Cancun, both very good with small chartes, very good people, make sure you let them know you are certified, bring your c-card, log book and a big smile.
Dive safe, have fun!!!
-Raf
Sorry for the grammar, i hope this info help you more than confuse you.