Nila,
If you really want to do this, I think nine buttons 300 x 200 a piece would be about right. If the buttons resize by screen definition, then these sizes are for 1024X768 which is the only res I use.
If they are to be user definable, I would use at least 3 for play lists. If not could you set the last 3 for PL-1, PL-2 and PL-3 playlists? That way before a day in the truck I could rename any 3 lists to coincide with these or maybe have 3 lists with those names and drag the contents of other playlists into them (kind of like setting radio station buttons depending on what city your in).
The other buttons seem like they sould be:
Stop, play/pause, last, next, remove currently playing.
Course you most likely have a better grasp of MJ and a lot more experience using it so if you have better ideas, I'd love to hear them.
BTW, will the trouble with command line operation I'm having now carry over to this project?
Could MJ8 be too buggy to do any of this?