Powering Arduino and motors on robot
It depends on the number of servos you want to use. Anything more than one is not recommended to run off of the Arduino's 5v rail. You'd need a shield like this one to properly run multiple servos, as you could connect a separate power source to the shield to avoid putting stress on the Arduino's power regulator. The shield could also run the motors you'd use in your project! The only other recommendation I have is to consider investing in a Lithium Polymer battery, as I've found those are generally better suited for projects like this.