Given that your source says that it was published in The New Yorker, I imagine the author is American.
In Europe, floors are described as follows: ground floor (street level), first floor (first floor above street level), second floor, third floor, etc.
However, in America, they call the street-level floor the first floor. So if the publication is American, then "first floor" will be the ground floor.
As for "down the hall" it means "along the hall" in this context. So it's further along the hall, not necessarily at the end. It could be at the end, but all it says is that it's closer to the end than the current position is.
Here's a diagram for example:
Doors 1-3 could be described as "down the hall" from a person standing at X. Door 5 is right next to him so it wouldn't be described as "down the hall". Door 4 probably wouldn't be described as down the hall since it's a bit too close, but it could be.
This rushes refers to rushes on the floor. She hops down to the rushes means she hops down to the floor, which is covered with rushes.
rush: a tall plant that looks like grass and grows in water. It is used for making baskets and covering floors. (Macmillan Dictionary)
The practice of covering floors with rushes in the Medieval times is mentioned on Medieval Hygiene:
Threat to Medieval Hygiene - Rush Flooring
The practice of covering floors with rushes was a a real threat to hygiene and health during the Medieval times. Following the Black Death a limited number of carpets and mats were introduced to replace the floor rushes but floors strewn with straw or rushes were still favoured. Sweet smelling herbs such as lavender, camomile, rose petals, daisies and fennel were added to disguise the bad smells which were prevalent due to the inadequate plumbing systems and the rushes.
See also:
Best Answer
The style of "on went" suggests that the person who is donning these articles of clothing is being quick about it. Compare "a whirl of skirts".
If someone were slowly removing articles of clothing, in a seductive way, for example, one would not write "off went the hat, off went the skirt, off went the blouse..."