As others have said similar, the PADI OW course doesn't really prepare you for very much... Get out and go diving, lots!
U/W photography can be great fun but you need to be a good diver AND a good photographer at the same time.
The easiest U/W shots to try are wide-angle in clear water but beware, even clear water is full of specs if you fire a flash into it.
The other style is macro and this is where your bouyancy really needs to be spot on... You don't want to crash into whatever you're shooting, or hold your breath and suddenly float off to the surface with a burst lung!
Small compacts (if you can get one which shoots RAW) will do you fine for a while, otherwise the gear gets very large and bulky! My ikelite housing, dome port and strobes take up practically as much space as the rest of my gear!
Check out Yorkshire Divers for a good diving forum with a nice photography section (a number of members on TP too), DigiGreen for a uk u/w photography site and Wetpixel dor a US one. BSoUP are a British group devoted to U/W photography.