I ended up adding a bit more to the left side of the apartment. I decided I just wanted more closet-mirror without shrinking the small space by the stairs. It hurts the sense of tightness I wanted, but the first floor was already much wider at the entryway space than I pictured. I may raise a wall behind the loveseat and turn it to a half-height display shelf. Or maybe place some bulky air-heat unit there instead.

Regardless, I think I've done enough measurements to get started. I will probably run some material experiments to see how I want to handle carpeting, next.