No standing army, but instead all wars are fought with mercenaries... Suits the new government, but it's definitely a risky venture. Adding Rome to your territory would all but solidify your claim to the rest of the world.
It mainly arose as a need to combat the various factions in the Republic and the external claims: with the money the Republic has, two large mercenary companies can defeat almost any standing levy army. Though they do deplete the reserve pretty fast...
The future looks Roman!
This discussion might be helpful: https://www.reddit.com/r/CrusaderKings/comments/2t68pq/mod_question_roman_republic/
Interesting ideas indeed!