Echoing the previous responders, adding an underwater camera hugely multiplies the task loading at every stage in a dive. You want to be sure that you have more than just basic proficiency with the fundamental skills - they should already all be second-nature.
The fact that you will be spending much of your time staring through a viewfinder, and preoccupied with thinking about photographic subjects and technical decisions, also makes you intrinsically less reliable as a dive buddy. I never bring a camera if I'm diving with a relative beginner.
PADI doctrine aside, the reality of u/w photography on most liveaboards and many shore-based operations is that you will sometimes find yourself alone, whether by choice or involuntarily, as your buddy or the group moves on while you are engaged in making a photograph.
This means you need to be more self-reliant u/w and capable of self-rescue, if necessary, and you may want to consider ways to improve or increase the redundancy or reliability of vital gear. Since you're more likely to find yourself on your own, it's also vitally important that you carry your own emergency surface signalling equipment - a big SMB, or sausage, a whistle, a good light or flashing strobe, and perhaps more - on every dive. Everybody should, but many don't.
(For more on surface survival equipment and techniques, take a look at this article, which originally appeared in the 2002 Annual Edition of Asian Diver:
http://www.tabula-international.com/DIV/SMB4i.pdf
I don't want to knock PADI so-called "Advanced" Course, but it's badly misnamed. Taking this course will not make you an "advanced" diver. The reality is that this course just provides a few more supervised dives in a somewhat wider range of conditions - one so-called "deep" dive, a night dive, etc. - than you will have encountered in BOW training. . That's not a bad thing in itself, but I think you will probably want to get considerably more experience u/w under your belt before you think about taking a camera down with you.
One PADI course that I strongly DO recommend is the Rescue Diver course, which provides training in some very important basic skills and should dramatically enhance your capability to assist yourself or another diver in an emergency.
Frogfish