i think the decision between single-stick and dual-stick is mostly one of personal preference. now that i think about it, single-stick might be more intuitive for new drivers, but i feel weird driving anything but dual-stick, and dual may give you more precise control.
if the driver needs more controls and both his hands are full, you should consider foot pedals. read ALL of Section 4 of the
OI reference guide to make sure you understand how everything should be wired, and then build a pedal with a potentiometer, pushbuttons, or some other method of input and hook it to the appropriate port. a good application of foot pedals might be to control retractable casters -- your foot goes down, the casters go down. very intuitive. use your imagination! extra points if you have a pedal labeled "distortion" that makes the robot play Jimi Hendrix cds REALLY LOUD!
~Aaron