@Nogus101 I like the Idea of a two-pronged attack, but I feel it would not be advisable for taking Arretium, as we would be moving troops through enemy territory. We would lose surprise when we attack Veil, and would undoubtadly meet resistance. We would also run the risk of the supply train being stopped and starving the troops.
Unless we can do it quickly, say with cavalry, I feel it would be unwise.
Another suggestion would be to do it when taking Vetulonii. From there we can send a portion of the army from Veil, and a portion from Volterra, while we send troops from Arretium to capture Milan.