I am currently playing a VH/VH campaign and I want to emphasis a minor point someone mentioned above. Wait to attack the Scipii in Sicily until AFTER the Romans are at war with the Greeks. I attacked on my second turn before this happened and I have since played the entire remainder of the campaign as the only enemy the Roman factions has ever had. I managed to hold onto everything but Sardinia, but it was touch and go sometimes. With all 3 Roman factions' armies only concerned with you and the Senate's fleet harassing you as well, this puts a major drain on your resources for other areas. I have still triumphed and am now preparing to invade Italy proper with Sacred Band and Armored War Elephants, but I think I made the situation much more difficult for myself than I needed to.

One final thing, it took me two restarts to survive the initial challenges of the Carthage campaign. On my first two tries, Cordoba was bribed by the Spanish and there was nothing I could do about it. The third time I was preparing to evacuate my army, but the diplomat got there first. Over several turns he failed to bribe my general, each time increasing his anti-bribe traits until his price eventually ended up at 500% of normal and they gave up. That was all luck, but as long as that army doesn't get bribed it should be able to hold on without problems. Without any outside support Cordoba (and a little good generalship) is able to hold off both the Gauls and the Spanish. Turn the city into a military base, pumping out those round shield cavalry. Also be sure to regularly check the province for Baeleric Slingers which sometimes pop up as mercenaries. Once Cordoba is upgraded to Stone Walls, those slingers will keep it from ever falling. Once the city is secure, behing making sorties against enemy armies. I was able to adopt two captains this way which gave me three generals in the region without ever needing to import any troops. Eventually my Spanish forces took the entire Iberian peninsula and are now pushing into southern Gaul. They are totally self-reliant and have never received any help from Africa or Sicily with the exception of a few young generals imported after the peninsula was secured to manage some cities.

Don't give up on Spain!