Question regarding gap between stair tread and skirt
No it varies by each step. There are about 10 steps between the landing and the top of the stairs, the gap is the largest (picture I posted) in the middle of the flight of stairs. It grows narrower as it goes down to the base stairs, or moves up to the top stair.
When I removed the carpeting, I could see that previous owners had a ton of caulk shoved in the gap. It looked pretty horrible, but also could have been because the caulk was old and yellowed.