I agree -- if you are thinking about doing Fundies, just get the 7' hose to begin with (although hoses aren't expensive to replace). Use a knife or a pocket to contain the hose until you have a canister light. I have never found tucking the hose under the harness waist strap to work very well -- it always seems to make its way loose.
As far as the hose on the backup reg, I think lengths vary a bit. I find 24" to give me an annoying loop of hose out to my right and behind me, and I'm seriously thinking of replacing it with a 22" Miflex (if they exist) to make everything lie a bit neater. But you can certainly USE the 24" hose which likely is the hose your primary regulator originally came with.
As far as the hose on the backup reg, I think lengths vary a bit. I find 24" to give me an annoying loop of hose out to my right and behind me, and I'm seriously thinking of replacing it with a 22" Miflex (if they exist) to make everything lie a bit neater. But you can certainly USE the 24" hose which likely is the hose your primary regulator originally came with.
I guess there are pros and cons for each configuration and as with everything else, there's no universal 'Best method' to use.
