you will only need 1 ipac for a rotating control panel because the wires can run from one panel to the other inside the enclosure.
and trackballs are needed for trackball games, some of the better ones are millipede, marble madness, bowling games, golden tee, too many to list. If you have mame32, open it up and organize the roms by wether or not they use a trackball, go through the list and see if there's anything you like on the list, chances are the games that use a trackball will be much more fun with one...