I've had both factions attack me, or do a DOW, in several campaigns, but it's not been that much of a problem getting past them - as long as they are they only two you are dealing with.

I play on hard, no Mods, and will focus on building up my economy the first 10 to 15 turns while taking out the Etruscans. I build up Legio I to around 16 units, Legio II to 10 units and start Legio III in Rome, around 8 units. I also build up the Classis I fleet to 6 or so units. Legio I and Classis I take out the Etruscans then moves back to North Italy by turn 7 or 8. The fleet stays on Sardinia.

If Carthage attacks during this time Legio II is strong enough to take on most anything coming their way, especially if reinforced by a city garrison. Since it's the early part of the game all units are basic.

Legio II in Rome is strong enough, again with city garrison support, to defend Rome and Naples from seaborne attack.

As long as Greece doesn't decide to jump into the mix you're OK. Gets "interesting" very quick if they want a piece of the action early on.

:)