Re: Your reasons for choosing a specific Roman house for a Grand Campaign as Rome
Uusally, I go north against the nearest Gauls until I hold the territory on the Italian side of the mountain passes (and maybe Illyria) and before going for Carthage (or possible somewhere else, depending on the state of other factions at the time.)
You're right, conquering the Gallic lands can wait, and yes, it helps to attack Carthage when they're ar war with nearby kingdoms.
I escort my transports with a fleet, too - and I know what you mean about the effectiveness of warship rams on transports. When I play as Carthage, I usually try to intercept Roman legions at sea with a half-stack fleet of Carthaginian warships.