Well, historically Roman situation was even worse -- they built up their navy during the war, and did it again and again. Pigs can replace Fish in Roman diet for few turns , but eventually one can get those Triremes going. It is a 4 cities vs 2, don't you forget that. Why would you attack first? With 2 extra cities time is running in your favor. Start 2 Triremes in Roma and Pompeii, possibly another one in Illyria, use Mediolanum for ground troops. Your terrain is better. No way to win attrition war as Carthage if Rome plays his cards right.