Regarding stairwells... what I recall is that some are, some are not. That seems to be the case as far as I can see on Google Maps as well. There is occasional noise from upper floors, like tromping of feet or dragging of chairs. I will request 'top floor' in my reservation (which they find odd since most people don't like to climb, possibly, two flights of stairs) but that's my preference. There is a booking category called "Hospitality House" which are eight building close to the HH, which is has most of the amenities including the boat dock to Disney Springs. There are non-HH buildings that are just as close (62, 63, 64... among others) that you could request outside the HH category.
If you want a quiet area (in addition to a quiet room), I've heard that the buildings in the lower right corner of the map (54, 55, 56...) are quiet... less traffic/people noise. I haven't stayed there so I can't vouch for it.