With the recent chages, you have to be careful, becasue armies consume food too, and food management for rome is always a pain, but yes, you should not upgrade all of your buildings, at least the ones that consume food, untill you have a steady food supply.
You dont have to build farms everywhere, and fishing ports are really bad, provide 6 food for -4 Po. Not worth it, build a lvl 2 trading port instead and a farm, farms at lvl 3 provide 9 food if i remeber correctly, for -4 Po, and even delicatessen is better than fishing ports.
So if you build have a lvl 2 settlement a lvl 2 trading port a lvl 3 farm, and a lvl 3 temple of neptune you should be alright, producing 9 food and almost no public order hit.
Last time with Rome i dedicated Africa province to food production. 4 fishing port at max lvl, 3 lvl 4 farm, 1 delicatessen, and temples and circus, i managed to Po around 100 with bread and games edict, and a dignitary, and produced around 40-50 food. Only upgraded the non food consuming settlements there.
You have to check your food supply time-to-time, and if its lower then 20, you should raze conquered settlements (or tear down everything after occupation), because you can go quickly below 0.
I hope that helps!
