Originally Posted by konny
Sea trade makes the difference. With the Romans all your towns have access to the sea and have sufficent trading partners all around, either other towns of yours or big foreign cities like Carthage. For example, with Taras alone you will make some 2,000 mne in trading short after conquest.
With the Seleucids most of your towns are midland or along coasts where no good trading partners are around. From an economic point of view you should concentrate on the West: Secure all around the Aegean including the islands. With the mines and the sea trade you will make enough money to run your empire.