Re the foot sensors, Lynxmotion have them for their hexapods
http://www.lynxmotion.com/p-626-hexapod-foot-sensor-pair.aspx
http://www.lynxmotion.com/p-728-tubing-foot-switch-kit-pair.aspx
They are designed for a tubular leg but you could probably adapt them.
Lynxmotion appear to have some real nice chassis as well if you haven't already bought the DF Robot one it may be worth looking at them.
Rob