The reason Powhatan dresses in his "greatest braveries" to speak with Smith is that "Powhatan wants to impress and intimidate Smith."
This is based according to the description of John Smith in his book titled "The General History of Virginia"
Also, the reason Smith feels the courtiers treat him as "a monster" is that they looked at him in an unusual manner which can be attributed to his weird and odd clothing style and his skin color because many Native Americans at the time have never seen a European man before.
