I did the show a few years ago with a cast of 10 (+1) - 3 things we did that may help:
1st - I made the character of Compere a show girl which gave me some really nice options for the scene when Mr Memory dies & creates another larger role for one of your girls, as a girl.
2nd - the train scenes work really well with additional passengers & officers, it was the only scene we did with all 10 cast members in it, although not all were named characters as I wanted to keep the bit with the salesmen/news boy/officer/conductor/old lady (w/ 3 actors) having them switching in front of the audience.
3rd - my +1 was a piano player who did all of the music live on an upright piano that sat against the stage. He also did several of the sound effects (train whistle, slap stick for gun shots, etc) & interacted with both the cast and the audience.
Hope that helps