We are definitely getting alternate outfits.
We are NOT staying in the academy forever.
My bet:
We will be in the academy early game where our cast meets each other and learns their classes. This is just early game stuff to establish the world and setting.
Then either via graduation or a devastating event we all depart to different continents do fulfill our duty based on what we studied at the academy, then there's a time skip before the real game begins.
On our journey traveling the continents, we meet back up with our allies from the academy and that is what builds our party.