From what I remember of your stage costume, most of it was cut fairly close to your body, and was specifically meant to not overheat you during performances while accenting you and your movements.

For this, we would consider options with music notes and staff lines, perhaps a tail coat or something that could flare about you when you spin, a collar or hair decoration which expands your presence and might involve either magic or glittering accents.

A costume party tends to... mm. Exaggerate the theme of the costume even more than a musician's stage outfit. I am not certain I am explaining this properly. Did that make sense?