Even 5 gallon is on the small side for a good season in NC, assuming sun all day long and plenty of nutes. I'd say a good season in 5 gallon pots should yield 2 lbs or so in your region, providing you get them started in late winter so they're ready to transplant outside once the last frost of spring has passed. 10 gallon pots, add about 50% more yield and so on for 20 gallon pots.
I don't see any reason to use over 30 gallon for a first year plant with the sweet spot probably being 27.5 gallon (55 gallon plastic drum cut in half to make each end a pot, BUT that's large enough that they aren't so easy to move around any longer.