Use an Array of mp3 files which when on keyPressed plays a random selection from it at the same time

I know it seems convoluted, Im struggling to play more than one track at a time using minim. I would like to know how to set up an array of maybe 10 tracks I have (bass,chords,melody etc), then on a key command to play a random selection of maybe four of the ten tracks at the same time, ?

Is this difficult to do? Any pointers very much appreciated.