Lutus,
Just to clearify, the UltraStik does NOT come with the wiring for the 8 buttons, you have to buy it extra (I believe it cost $8) You could make one yourself if you want, it is a 10 pin molex connector that connects to the UltraStik header under the joystick. 8 wires, one per button, which will need to have quick disconnects added or you will need to solder and 1 common ground wire that will need daisy chain to each button.
I bought the UltraStik just a few weeks ago as I just got back in the MAME scene and am making a new MAME box. I currently have the UltraStik up and running as a solo CP. With eight buttons (7 to play and 1 "Special" Key) I have been able to map all buttons for MAME and Mamewah to work WITHOUT the need for any encoder (although you do need to modify the controler files)! I am working on adding Console emulators next.
I have not added a track as of yet, but want to. I was thinking Mini-PAC at first, but Havok is right, it is a waste of cash just to add a trackball to. I think I may go with Ultimarc's stock trackball and an optipac. Andy says that the Happ's 2-1/4" replacement balls are identical and will work in his trackball housing, this way you could buy a different color ball than red or white (happs 3" is ~$100 and Andy's is $38 + $16 for a Happs replacement, still cheaper). Keep in mind if you go with a smaller trackball the CP could be more "Lap" size rather than "Desk" size. I am going for Lap myself as these are just mock ups mainly for testing till the Upright cabinet is complete.