Learn English – meant by “got jumped”

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.

Figured out means "understood" or "solved", as you noted. I think the problem here is with "it" or "it all".

"He's got it all figured out" would, in general, means "he's got life solved" and would imply that the person has worked out a successful way of living. In this context, it would go beyond merely making a lot of money (because that was explicitly stated) to being happy, having success in other realms and so on. Someone making $1,000,000 a year but who was miserable would not have it all figured out.