5. what does the staff represent?

Excellent question. Of course, the staff is first introduced as belonging to the shadowly gentleman that first meets Goodman Brown as he ventures into the woods at the beginning of the story. This gentleman is obviously meant to stand for the Devil, and his "remarkable" staff clearly indicates the way that this is suggested, coupled with the way in which this man constantly urges Goodman Brown to travel deeper into the woods with him. Note how the staff is first described:

But the only thing about him that could be fixed upon as remarkable was his staff, which bore the likeness of a great black snake, so curiously wrought that it might almost be seen to twist and wriggle itself like a living servant. This, of course, must have been an ocular deception assisted by the uncertain light.

However, what is interesting is the way that this "staff" is carved as a snake, which is of course a symbol of temptation and evil. Note the way that this man constantly offers Goodman Brown his staff to support him on the journey. Also, note what happens when this man gives Goody Cloyse his staff:

So saying, he threw it down at her feet, where, perhaps, it assumed life, being one of the rods which its owner had formerly lent to the Egyptian magi.

The link of this staff to the ones that the Egyptian magi used in their contest of power against Moses in the book of Exodus in the Bible clearly indicates the way that the staff is associated with evil. Let us just consider briefly what we use a staff for. A staff is used to support us, to give us strength and to aid us, making journeys easier. Clearly, if we put this together with the presentation of the staff in this story, it is strongly suggested that the staff therefore represents the act of relying on evil to support us in our lives.

The devil’s staff, which is encircled by a carved serpent, draws from the biblical symbol of the serpent as an evil demon. In the Book of Genesis, the serpent tempts Eve to taste the fruit from the forbidden tree, defying God’s will and bringing his wrath upon humanity. When the devil tells Goodman Brown to use the staff to travel faster, Goodman Brown takes him up on the offer and, like Eve, is ultimately condemned for his weakness by losing his innocence. Besides representing Eve’s temptation, the serpent represents her curiosity, which leads her into that temptation. Goodman Brown’s decision to come into the forest is motivated by curiosity, as was Eve’s decision to eat the forbidden fruit. The staff makes clear that the old man is more demon than human and that Goodman Brown, when he takes the staff for himself, is on the path toward evil as well.