I did my AOW on the U352 last summer after about 60 dives to 60-70 feet, and I have to admit, that although I was fine once I got to the bottom (115 fsw), I was anxious at first. My 2nd dive was great, although I dove air, it was a very short 12 minutes. I would suggest nitrox training to maximise your experience on the bottom.
My bigger concern than the being comfortable in the water and on the bottom is your comfort level on the boat, and getting in and out of the water. 90% of my dives are from small boats in the ocean, and being on a large dive boat had a whole new set of challenges. But I have been boating all my life, so being in on the ocean on a boat was something I was already comfortable with.
See the thread in basic scuba discussions about the transition from quarries to mid-atlantic ocean diving.