As a guess--via the latest drone footage:
The entrance and exit seems to primarily be on the first floor (entrance around Studio Deli and the exit in-between the restrooms and Jurassic Cafe), with the mountain blocking the 10UCP facade. There should be an staircase around that mountain, and closer to Bowser's Castle.
As far as a potential expansion, they could have a form of a passageway on the second floor set that'd connect SNW to Soundstages 16-20, for while not a large expansion, something new.