Trace your pathways everywhere you might need to go. Outside, to the gym, to the cafeteria, to the loading area. Make sure you have 48" doors or double doors with an easily removable (with a key, no tools) center post. Call it a "mullion" if you want to be fancy.

Power in the floor near your planned podium location.

Several power outlets on every wall.

Sound system built in that puts the metronome behind the band, controllable from the podium.

Big industrial shelving for equipment. We have the Wenger GearBoss stuff, it's stupid expensive but it's great.

If you're marching, think about props. Where will you build them? Where will you store them? A big roll-up door from storage to outside makes that easier.

Think about where your offices and practice rooms are. Ideally you would have line of sight to the practice rooms from both your office and from your podium.