The wiring is pretty easy as long as you dont wire up the entire thing and turn it on. IE, test it out as you go.
Things to remember. You can daisy chain the ground. IE, send the ground to a button, then a wire from that button to the next. But the ground MUST go back to whats controlling it (ie, the ground from an IPac shouldn't go to the ground of a hacked joystick).
Next, how are you doing the spinner/trackball hacks? Optipac? hacking a USB mouse? Each one is different and takes thought. You mentioned optipac, so I will do a quick assumtion. The optipac connectiosn and settings will be based on what trackball you have (or what encoders you have). I think there are three or so different settings that people use to get them going. Look at the site for info directly for that. The software if you have more then one trackball is the challenge.
btw, the easiest is probably the buttons/joysticks. get them working and move to the trackball, then spinner.. No need in trying to get them all working at once.