To make the game totally accurate is to make an unplayable game.

The history is very fascinating however, Sulla and Marius fighting over the rights of the people, Sullas brutallity in victory, Cato the Younger refusing to outlive the Republic, Brutus forced to kill a friend so close to him they were like father and son, the last stand of the betrayel to Cicero and the Republic by Octavian, Pompey the Great betrayed by a dynasty he had saved from destruction.

On the Catholic Priests you don't know what they do yet. It is accurate for them to come along to give special morale benefits, and the christian empire consistently had priests along with the army to do burial services for troops, baptisms for their children, explain to the troops how fighting to save Rome is pleasing to God and other non battle activities, so having them along (Probably just to sing prayers for the troops to increase their power and be really weak) is not innacurate.