1) he has free will and could have chosen not to do what he did
2) when he said," that is a step i must fall on or else o'leap." before he ever spoke to Lady Macbeth on the matter is proof of his own greed.
3) He manipulated Lady Macbeth, as if you read his letter he repeatedly used language that implied how wonderful her life would be of she was queen, and said nothing of his own opinion on becoming king. He manipulated her into 'persuading' him in an attempt to ease his own conscience
"The fight" is the main noun of the sentence and the pronoun "it" was used refer to the noun. Also, it's the last (and only) noun mentioned before the pronoun.
