Pianonator,
I think you will find building your navy to be a real key. You can really inhibit the military operations of your enemies. Blockading their ports puts a serious dent in their commerce. The Brutii are vulnerable there. Personally, I can't imagine winning the long campaign without naval supremacy. I'm sure some have done it, but I can't envision it myself.
If you're producing real quality units, the Gauls should be a pushover. If the Brutii are showing some real quality troops, you have a nice healthy challenge on your hands. I'm playing a long Julii game at the moment, but would like to do a long Carthage game so I can try out the elite units. I've been setting up some custom games at normal level and hard level. I tried out Carthaginan sacred band vs. Spartan hoplites. The Carths won, but the Greeks are weak in cavalry. I think the hoplites would have fared better had they had some force on their flanks that they could depend on. I want to try Gaul royal swordsmen on Praetorian cohorts next. The Roman factions' wide variety of cavalry makes them an extremely formidable enemy if you take any of the other factions against them in campaign. And their infantry are tough hombres too. Such a variety.
Keep us posted.
Guyus