One of the Sicilians name is Provenzano, this is the name that the real life undercover officer used to bring down mafia hitman, Richard 'Ice Man' Kuklinski.
In the scene where Tommy gets Brandy's son his medicine, the Pepsi fridge in the background has a blue Pepsi bottle on it. The label was changed late 90's. In 1991, when the movie is set, it should be the more classic white can.
When Tommy enters Reggio's mansion he clearly gets shot in the right shoulder/arm. His arm just hangs at his side and subsequently he carries his gun in his left hand. When he reaches the basement and finds his brother Vincent he is shown carrying the gun with his right hand with his left arm being limp. In the same scene he finishes clearing the room and has mobility in his left arm again to grab Vincent. Then when he gets shot in the back he is back to having a limp left arm and shoots the bodyguard with his right hand.