1) If he became President, how much power does he have realistically to force passivity re: Iran?
No President has any power to realistically force Iran to become passive. The Iranian regime stays in power by stirring up nationalism and anti-Americanism when the United States acts aggressively against Iran. Thus, anything short of an outright invasion followed by nation building will not "pacify" Iran.
2) I've heard him say he doesn't really believe they are a threat because of their physical position etc. and that he also believes they are not close to having nukes but I've heard many others say they are close to having nukes. I believe I've heard him say that the only reason they want nukes is because we're scaring them into thinking they need them and they should have them if they want. Is this correct?
The US has military bases all around Iran - to the West in Iraq, to the East in Afghanistan, to the South in the UAE. Also, the Iran is surrounded by nuclear countries, some of them friendly to the US: Israel to the West, Russia to the North, and Pakistan and India to the East.
3) Do you believe he believes that the leadership in Iran can be reasoned with?
I'm not sure what he believes, but if we can reason with the North Korean dictatorship and we managed to reason with the Soviets I think there's hope for Iran.
4) Do you think that if he became President and was exposed to classified intel he may not have access to presently, that it is in him to change his stance on passivity toward Iraq?
If Iraq posed a clear and present danger to the United States, then yes, that would change his view. However, what do you think the probability of a third world country posing a clear and present danger to the United States is?