i tend to do a 2:1 surface:dive intervals. but then again most of my dives are 1:30-1:40 and in 50-80'. the fishing on the BC coast gets dramatically better the deeper you can dive. sure there is a lot of wasted time going up and down, but if that's where the fish are....
Wally, been telling you for a long time now, don't over think it, just get out and dive. you're new to the sport, the best way you can develop as a diver at this point is experience. dive dive dive.
as was said before, fitness will play a major factor in your enjoyment of this sport. for me, staying in shape is the biggest bonus to spearfishing. if I didn't care about fitness I would eat twinkies & drink beer all day and hunt on scuba (flame on!)
and Waldo - wait until spring before you shell out for a dive comp. if things go to plan I'll have my D3 for sale by then.