So exciting that this will be your first
Disney Cruise! It sounds like you've done some research on the standard operating procedures of the other Disney ships. And mostly it seems like the Adventure will follow most of these procedures. But since the ship hasn't begun sailing with passengers yet some things will be more clear once those sailing start.
Typically the fastest way off the ship is if you carry all your bags off the ship (instead of having your room steward take them the night before). I assume it will operate similarly on the Adventure.
Yes, the shows are first come, first serve for seating. Again, Disney has never had a ship this size so maybe the showtimes will be different or offer more showtimes to accommodate the number of guests. I know when I've sailed on Royal ships of this size, the same show is offered more than just 2 show times (but on a 3-night sailing there are only so many options). Again, there will be way more info in March once passengers start sailing (or before then).
I'm sailing the first week of April and will report back (but I know many reports will be available from March by then).