Copper tubing will in time corrode with the propane . If the copper tubing is left untouched it generally wont cause any problems like the pigtail used to hookup the larger tanks for household use. If that copper tubing is tampered with it can result in a flood small flakes that can clog orfices and gas controls. If you are moving your system around frequently or automating your system later i would look at something else to plumb with..
If you are using the the regulators as they were posted originaly, the qcc fitting (black, red or green female connector to propane cyl. service valve) have flow limiters built in based on color. green is highest a p.o.l. fitting could be installed in its place leaving your regulator as the prime source of btu limitations..