You seem to have a lot of experience with this?
Heh! I've only got so much experience as one can accumulate from failing several times, so take my recommendations with a grain of salt. I'm only working with the research I started about a year ago, when things really fell apart in my life --and then went downhill from there :-P
I let others decide what position works best for them. I think the cautions I've heard about sitting up vs. lying down have been a bit more precautionary than they
might need to be...? It's all about avoiding displacing the bag before the gas has done its work, and knowing that, it's all up to you. If you try lying down with your bag on, and then twitch about to the degree you are familiar with, and the bag isn't displaced, or the elastic pulled open, I'd have trouble arguing with you that lying down wasn't a good idea.
I wasn't even gonna get a regulator, cause I was going to buy two of the disposable tank sizes. I think they're like 14.9 measurement units. And just open each valve til I hear the gas flow.
I
strongly recommend against that approach. There's no telling what your gas flow will actually be --you simply can't tell by the sound, and it will fluctuate as the amount of gas in the cylinders decreases-- and you don't want to run out too soon.
I'm not sure where the best source for info on cascade systems are. I think you could probably do a search for <gas cylinder cascade system> and come up with something useable. At it's most basic, it involves hooking the tanks up in series through a common regulator, but the hardware requirements can get complex because you're building a tubing system that needs to withstand the full pressure of the cylinders
before it reaches the regulator.