Thank you so much. I reckon playing this enough will definitely make you better at it yourself as well.
(As an aside, I’m curious why you start the players in a stadium - is this a station large enough to house sports events?)
No particular reason, but it does help the DM assume a scale of the place. The larger the stadium, the more apparent its significance, the greater possibility of another one, etc. It could've been anywhere, like a theater or some cargo hold, but a stadium does provide a sort of walled area by its nature and demands a certain minimum scale.