Building walkers is all about making tradeoffs between weight, servo power,
battery power, and cost of multiple servos. All fun. After selecting something
long these lines, you might try adding up all the weights and projecting about
how long the legs can be.
I am going to assume that the Arduino motor shield won't be the solution. It only supports 2dc motors? Anyone know of a good one that like someone said, supports 18 servos and additional sensors.
Motor shields support D/C motors not R/C servos.