We've been told in the past that P1-P2-P3-P4-P5 order matters. Just how much, nobody (other than the developers) knows. But P1 has the most impact and P5 has the least.
In your example above, in order of best to worst: Player 1, Player 3, Player 2, Player 4.
Catcher's PC is a modifier. It would affect each pitcher the same.
I forget exactly where the cutoff is for when a pitch is a help or a hindrance. I thought it was around 30. There are rare instances in which a pitcher's current OVR rating is slightly greater than his projected OVR rating, and in all those cases it's because he has dropped (from his current ratings) a low rated P5 (which still shows up as projected P5).