How about a concert version of something? Pick a show - have a few kids (those who don't sing so well  ) act as narrators to "tell the story" between songs - have a few soloists sing the solos (because it's a concert, you don't have to have one person sing all one character's songs) and the larger group sing and/or dance the big numbers.

Another thing that can be done is pick a musician - or a style music - or a composer - and arrange a concert that is a 'valentine' to a specific person/style. Cole Porter, 1950,s, Broadway, etc.

Sounds like a challenge - good luck!

Yes, you have to pay royalties on songs.  Moreover, you have to ask permission from the owners of the songs.  We just had a show close locally because a community theater tried to put on a show with a bunch of Broadway tunes.  There are a lot of pre-1923 songs that are in the public domain, but you can be nailed if you try to do famous Broadway songs.  You'd think they'd be more generous with non-profits and schools, but that ain't the case.