Crazy Promposal

My sister's boyfriend is a very talented musician. Last year, before he was her boyfriend, he planned and carried out a very sweet "promposal" to my sister for their junior prom. This year, for senior prom, it had to be bigger and better. He gathered a large group of his musical friends and had them fill out surveys to ensure they were truly committed to the project. From October to March, he held 25 practice sessions (at his house; his parents are saints). He had teachers and administrators involved to ensure that nothing was going to mess it up since he was doing it during a class. And here it is: