My main is actually a food city. I have enough lumber and iron cities to send res to main main to keep building. At 1st my main had lumber and iron 60/40. But then after sending more and more res to my main, it stopped producing anything as the city was always over cap limit. So just decided that if it isn't gonna produce anything then might as well have farms to make it easier to maintain a slightly larger army. Atm my main is cutting my upkeep by 2mil. Not much but that's 48mil less food I loose a day so im fine with it.