Some of the decks don't have windows and those that do are floor to ceiling ones, what you highlighted as one deck is actually two decks deep.
No. You can clearly see the curved corridor wall through the opening and it's twice the height of the windows on the same row.
Also notice you can only see one row of the rectangular "coffin" wall depressions through the windows, which would not be the case if the windows were the hight of the entire corridor.
It's more obvious that that's one deck when you see it in motion:
There's one wall, affected by one light source, with no floor or celling dividing it in half.
The saucer is at least four decks deep at the very least possibly six.
Based on the scaling of the bridge, atrium and shuttlebay, yes. What we see in this shot is not.
We already know ILM used multiple scales of ship in the first movie (the 350-ish meter ship used in the shipyard scene, for example). This is evidence that they've done the same with this movie.