Will upvote answers
what is the narrator’s primary reason for coming to the house of usher?

to meet madeline and determine the state of her health
to visit and comfort an old friend from his childhood
to ask the doctor how to medically treat usher’s condition
to confess his financial problems and request a loan from usher

to visit and comfort an old friend from his childhood

Usher wrote to the narrator asking him to come to cheer him up. The narrator comes to the house because of the request of his friend. He wanted to provide comfort to his friend in his time of need. He was unaware of Madeline's health and he did not know the situation he was walking into. The narrator has no intention of talking to Usher about his own problems.

well stockyards mean a large yard containing pens and sheds, typically adjacent to a slaughterhouse, in which livestock is kept and sorted. and i'm assuming that by party you   mean a large group of people which does make sense because chicago is a very crowded place much like new york. stockyards tend to take up a lot of room due to needing the area for pens to keep animals in and the fact that stockyards are usually right by slaughterhouse where they process and distribute the product. so its much like a zoo but with some dead animal products close by.