hey
my controller has 8 "pads", 4 push buttons (with 2 options: click or click+hold), 4 pots and then one more push button (that changes the notes for the pads - major, minor or pentatonic scales).
You can take a look at the thread here:
http://arduino.cc/forum/index.php/topic,98177.0.html
About the trackball i have no idea, but with the push buttons and the pots i think it should be quiet straight forward.
How many are you planning to use?