I really think all of your questions will be answered in your class, and ANDI book/DVD or whatever else you get from your class. Just ask questions in class and you will learn what you need to know.

The only question that will not get answered is your double 40's question.

Again back to the other post....stick with the single cylinder. You are going to add so much weight for the same amount of air/gas. I am thinking after you actually get some dives in, you will understand. If you are really going to go with doubles (and I think you shouldn't right away), then you will most likely want at least double 85's steel. There has to be a decent payoff for all of the extra weight.

I guess if you really want to be streamlined, you can take like 6 14cubic foot pony bottles and make a rig that wraps them around your belt area. You will be the laughing stock of the scuba world, but you will have your freedive feeling and still get a bit more than your 80 cubic feet. Just messing around with that idea, DON'T take it seriously.

Remember, you are not required to reinvent the way we dive in order to enjoy scuba.