1.  Dunno.  Notably, you don't "read" what Mike is going to say, you just select the social approach he will use in his response. 
  
3.  Melee is a skill in the game, and putting points into it/using it is optional. 
  
5.  You'll get to see some of it   I don't think you'd miss out on any major sections of the game, but you will of course miss dialogue and plot branches.