you should read Peter Heather's The Fall of the Roman Empire, which sweep away some common misconception about the late empire and the IV century in particular. Most of the recent research is going into the direction of a general rethinking about the idea of "decadence" of the empire.
Carthage was one of the main cities of the empire, and the economical engine of the western half of the roman world. Heather speaks of an "economical boom" of Africa under the empire. This will be reflected in the game.