I don't think J. Sack ever intended killing Tony. Its just safer to meet one on one and on neutral ground(in Sack's house that is Jersey, so in Tony's turf).

Sack is a very sneaky guy he plays Tony and uses him for his own benefit. Like the hit on Carmine sr. in season4. that could have caused a lot of problems for Tony and his family. Sack acts like he wll pick up the pieces but i doubt he would defend Tony if that ever got out.

But he also has his weaknesses like his ego, if he was smart he wouldnt have mentioned the joke Ralph made, but just made sure Ralph payed for it later. Being a New York underboss and Carmine's number 2 man (with his consiglieri in jail)it shouldnt be very hard to make it look like Ralph was stealing Carmine(which he probably was)and get him killed. Or blame Ralph for something else.