Well Frank didn't know the guy killed a dog, he just knows that he deserves punishment.
Not necessarily. We also saw visions of Karen. Basically its the thoughts on Frank's heads haunting him.
Because he is royally messed up right now. That's the entire point of that scene. Frank is normally a guy that gives a crap and steps up when he sees things going down. The fact he didn't in that case is meant to tell you just how messed up he is.
Ma Gnucci called them in from all over, and its not weird for a lot of gang members and hit guys to have weapons.
Just like Frank, violence with no purpose.
He was cleaning the tombstombs, a common thing people do when they visit dead loved ones.
No it actually makes PERFECT sense. Because this was always the end of the road for Frank. Its the classic message, Vengenance does not heal your soul.
Frank had "finally" taken out all the people that were even halfway involved with his family's death. He had gone through the entire roster. And so now he's just stuck, he's sitting there in his pain and grief with no purpose to drive him, nothing to distract him. Just the demons of his past tormenting him. And I want to say Jon Bernthal did some amazing acting in those scenes.
this is actually not uncommon. You take some tortured men and you give them a purpose, and there a wrecking ball. But once the party stops, with nothing left to do and distract, they just break in half.