1- maybe the fact that he saw his ****ing brother murder his family has something to do with the issues
Sorry, but I had a similar incident and I'm perfectly fine. Guess whose position I was in, Itachi or Sasuke?
Anyways, on topic :
1 what do you think sasuke's emotional and mental issues mainly stem from
His bloodline. He's an Uchiha, a group who tend to be emotional.
2 is his behavior justified
His behavior is justified. He just wants to kill, kill, and kill. He wants to cause chaos and destroy the system. He reminds me of my past self, but thats a different story.
3 if you had the chance to talk to him face to face what would say or do to "fix" him
I would tell Sasuke to destroy the Leaf. Defeating Obito and Madara isn't going to bring back Itachi. If you ask me, Itachi soiled the Uchiha name. I would've joined the Uchiha in destroying the Leaf. I say Sasuke should finish what they started.
Regardless of what I say, I would kill Sasuke after talking to him. Then I would destroy the Leaf and everything else with it. No offence to the Narutoverse or anything.