LPG Piping Questions

I am in the middle of a two tier brewstand build & have bought a HIGH PRESSURE ADJUSTABLE REGULATOR/VALVE
( http://www.agrisupply.com/high-pressure-adjustable-regulator-valve/p/64484/c2p/cs/ ) & 3 CAST IRON HIGH PRESSURE BURNER
( http://www.agrisupply.com/cast-iron-burner/p/30295/cn/5400000/ )

I am looking to pipe these together with soft copper & ball valves for flame control , is 3/8 copper large enough to handle all 3 burners ?

I have a 100 lb. propane tank outside the garage & would like to use LP GAS EXTENSION HOSE 3/8" 15' ( http://www.agrisupply.com/lp-gas-extension-hose-/p/39791/cn/5400001/ ) , would there be a problem with freezing from length of line vs. demand from burners ?

I'm building a single-tier with high pressure, too. Because most of the flexible hoses at the local box stores are low pressure, I'm also going to be using flexible copper from the valve (high pressure) to the burners, too. The valves only have 1/4" out, so I'm inclined to think 3/8" copper tubing should be fine. My initial tests indicate that there's plenty of output through that tubing. As far as firing all three goes, I wouldn't be too concerned. I doubt you'd be firing all three at wide open concurrently. In fact, I can't imagine having two on simultaneously that much in a normal brew day.