I think the Romani are the ones for the long game especially if you aim to one day get to14AD. Add some of the mods like City growth and Allied legions and play semi-historical, though don't be a slave to the timeline!
My fundamental house rule is only fight when attacked or to keep the balance of power, think spheres of influence. Try to keep all the other factions "alive", lots of big gifts and forced diplomacy help here, currently I'm at 209BC and all the other factions are still going, though the Saka are besieging the last Pahvla settlement! Difficulty is M/M which seems to help diplomacy and slows AI growth.