Ford is Arnold! He whispered it himself to Teresa! He says "Like I said, I built all of this" just before bernard killed her and after stating out loud "Arnold and I built all of it"! Multiple personality disorder maybe!

You forgot to mention one big thing, Ford is Arnold! He whispered it himself to Teresa! He says "Like I said, I built all of this" after stating "Arnold and I built all of it"!
Now I know why this IS Hopkins role!