Nice job capturing half of Europe. I just conquered Greece and Rome and I am Brutii(?) I need some tips because the other teams hate me. :(
Everyone always hates you really... no-one can be trusted, they all want your land in the end.
In my Medieval English game I ended up being at war with France, The Holy Romans, Russia, Venice, Spain and Denmark at the same time, I still won easy enough though.
In Rome; as Romans you can win nearly anything with legionnaires, even before the reforms, so as long as you have a few large armies ready not much should be a threat to you. Unless you've decided to go to war with Rome itself... then it'll be a bit more tricky.
The Roman factions are just all for capturing other places, so aggression is probably the best tactic, Rome's designed to be on the offensive.
To fund the legions I would suggest trying to get as much income from trade as possible, there's a lot of wealth there.