I think the chello works well in folk music and is underused. You might like to listen to the Tollpuddle suite by Graham Moore with Gill Redburn playing the chello.   

If you want your music to ' go into the tradition' it might be best to include a good dance tune that can be played by the majority of english melodeon players who tend to use boxes that play in G and D without accidentals. Spiers and Boden or Morris on might give you ideas. be aware that many melodeon players do not read music.

Why not check out what the Cambridge folk club is doing on that Friday if you are there anyway. They are a very welcoming lot but some nights are guests only while others are open stage.

Many melodeon players sing as well as play so you might want to include some voice in your composition.

All the best with your project.

Flora