I was going to comment on the similarity between the Sondheim theme and yours, but Ken beat me to it lol.
Generally it's a very well constructed piece, very upbeat, with catchy melodies, sharp orchestration, and interesting harmonies. I think it maybe a little TOO "economical"...I wouldn't have minded another theme, possibly something contrasting in mood, key, tempo. After all, rhapsodies are suppose to be more improvisatory with a range of contrasting moods. Also, since you feature the piano as a solo instrument, I was wondering if a bombastic cadenza towards the end would be appropriate?
Thanks for sharing, and nice to see you back on here!