1) Like Mediolanicus says, catapults were only introduced during the Roman empire. However, the ballistas used by the Greeks were far bigger than the current models. Unfortunately, the models for siege engines were never made (well, there is one old screenshot, but it's completely wacked out) and now the team has moved to M2:TW, there is little chance we'll ever see realistic models.

2) I don't think there is a clear-cut distinction. Getai was the Greek name for Dacians, but the Dacian kingdom seems to have been centred around the province to the north of the Getai. I guess one can make a case for both.

3) Actually, that's the reasoning behind the current requirements. You see, northern Italy was at this point inhabited by Gauls, while the conquest of Sicily would have brought the Romans up against the Carthaginians and their Iberian mercenaries. Off course, they had already encountered Greeks during their wars with Epiros and the capture of Capua, Tarentum and Rhegium.