All you need is a capable gouverneur for those towns, at least for the first couple of turns when the unrest is high. The theater in Taras will give your sharp and charismatic FM good anti unrest ancillaries ( like: Orator -2 unrest, Musician -1 unrest etc. ). It also depends on the temple - actually Ceres Temple is the best one in the long terms ( decent public order, great trade revenue from the larger versions, and a place for your "populares" to do something for the people ). The most important thing is to get rid of Greek gouvernment building - upgrade it to the next level asap. Concerning enslavement: i do not see it as massacre, just kind of proscriptions against anti Roman elements, while extermination is really ugly and doesn´t belong to the Roman way concerning the Greeks, actually. But you still can keep decent public order in Syracuse if you put taxes on "low" and got a high influence/skilled administrator gouverneur there. Client rulers ain´t an option for Italy ( or Sicily ), imo, unless you want to roleplay Syracuse beeing your ally during the First Punic War ( but i have to dissapoint you - there will be almost no resistance from Carthage against you in Sicily except one big battle once you move towards Lillibeo, since they are too busy conquering villages in the Sahara.... ).