If you have as many territories as you do, you should be able to make and support several invasion armies of first-class troops like Silver Shield Legions and Pikemen, along with Cataphracts or Companions, and maybe some elephants. With an army like that, you should be able to take out the Senate. However, if you feel you can't take on the regular Romans in their own cities, what makes you think you can take them on around Rome? That's the Roman heartland and where they'll have the ability to build their best troops, like Urbans and Praetorian Cavalry. I would encourage you, if you can, to build up a full stack or two of good troops and land in southern Italy, then just work your way up the peninsula. That'll secure your lines of supply and you won't have to worry about fighting on three fronts around Rome. Besides, once you've taken Italy from Croton to Mediolanium and Sicily, you'll have gutted the Romans, and the rest of the game should get a lot easier.
"Freedom is never more than one generation away from extinction." - Ronald Reagan
"Judge them not by the color of their skin, but by the content of their character." - Martin Luther King, Jr.
"Pick up a rifle and you change instantly from a subject to a citizen." - Jeff Cooper
"I like my enemies like James Bond likes his martinis- shaken, not stirred."
My first book, The King's Own