Training frequency is probably not as important as intensity and quality. Fewer, more intense training sessions with plenty of rest in between seem to work well.
5 days of pool training per week seems about right for me, any more and I risk overtraining. I do quite a lot of long swims (every second session) and it's amazing how much they knock you around if you don't allow yourself to recover properly. Sessions last about 1.5hrs. Bit like Jorg - no warmups, just straight into the dynamics.
And now for the contentious bit... I think that static apnea is irrelevant if you're training for CW or DYN
