Yeah it's a tricky one but one approach is to make one game focusing on 330 to 27 BC and then add some expansions extending the timeline beyond that to say 767 (up to CK2 Charlemagne). Add in a converter tool and prepare for a mega campaign 330 BC - 1821 AD.
Personally I much rather have game starting from 753 BC, so that we can play the interesting empire building part of the Roman (or Greek or Carthagian) history. I don't see much point of going past the early Roman Empire, because playing as Trajanus or Hadrianus will probably be rather dull, because no one has strength to oppose the Roman might. And playing as other factions is probably a suicide.