parts for arrangement

[Zoe Forest]

I am trying to arrange a piano piece for a full concert band for my school band. I don't have a whole lot of experience arranging pieces and the main problem I have is since it was originally a piano piece, there's only about 5, sometimes 6, notes/parts at a time but I have to write for 21 parts (3 clarinet part, 2 flute parts, piccolo, 3 trumpet parts, 3 horns, etc.) plus percussion. I have all the low brass parts and the melody switches between the flutes and clarinets, but I can't figure out how to incorporate the trumpets, horns, saxophones, or bassoons without having 4-5 instruments playing the exact same thing, especially since the rhythms in this piece don't vary much between parts. I don't want everyone playing the same thing and I don't want to give everyone really long rests. How can I give a part to the other instruments that still works with the piece without it sounding too cluttered or just bad?

[Dr KeyBaG]

Oh, really not my field to answer that... But I do know that Sibelius has a feature that allows you to get full orchestra arrangements just by adding the chords you use. Maybe that could be something for you?