Go up to post #2 in this thread and click on the link to Generac's generator sizing document. There's some good information about propane system requirements in that document.
I am currently attempting to determine if our gas system is sized correctly for a 10KW Generac system. We have a 1K gal bulk tank with a red high-pressure regulator on it, and a line (I'm guessing about 3/8") leading to the house, where there is a larger green regulator about 4-5" in diameter, labeled at 10 psi / 13" WC. The generator will be placed about 10 feet to one side of the regulator.
While our tank is large enough for this application (the generator and appliance (furnace, water heater, and cooktop) inputs are less than the tank's ability to supply vapor at 0°F, my question lies with the regulators and lines. I suppose our propane supplier, who will be doing the hookup anyhow, can determine this.