I don't know if it helps, but what I did was send a diplomat on a boat to cruise round the Med, negotiating trade rights with all factions and identifying their cities (can you only trade with a city you have uncovered on the map?). In MTW, sea trade was the big money-maker - not sure if it is in RTW, so I played safe.

As Julii, I found I could fight a light, Rumsfeldesque, style of warfare against the barbarians that kept costs down. Very few combat stacks - pretty much one per enemy faction. Each only 12 units eg 4-5 heavy infantry, 3 missile, 2 dogs, 2 cav + general in a stack. Then just 1-3 town watch for garrison. I would prioritise buildings over units.