Is this good enough for a 10gal system?
 

-20psi regulator, hard lined to three burners
-each burner is one of the 70k btu banjo burners from agri supply

I don't want to wait forever to get 10gal to boil, but I also don't want to waste a ton of propane... does this strike a good balance?

I'm not sure what type of valves I want to install in the gas lines to adjust the flow rate. Got suggestions?

Well, this will burn a bit of propane, but I imagine you'll be able to get around 3 batches of brew out of each propane tank.