[Oz Cello]

Depends how you want to use it. Is having the number in the title useful or could you do away with it? If it's useful could you have it in a different field? You could for example have the number in the 'custom group' field, then if you want it to be part of the displayed title you could format the title to show the number with the name of the song. If you need the numbers to order properly could you change them all to 3- or 4-digit number (001, 002, 003 etc)? If you are using the pieces in different groups then you might want to assign a 'collection' to each group you play with so that you can then filter your library to just show the pieces that you play with the group you're playing with at the time. You could also have a separate library for each group you play with.

How are you creating setlists? Searching while editing setlists works fine for me but you might be doing it differently.