Sorry, I do not have the CAD files for the robot. You might have better luck asking the original manufacturers: DAGU.
You could use the UNO. But make sure you have enough I/O pins to accommodate for the number of servos.
I do not think so. But in the Arduino IDE, ensure that you have selected the MEGA as your controller.
You can use an Arduino Mega. Or an Arduino Uno with a servo shield.
All the code and schematics are available in this instructable.
Use this resource to build one: http://www.thingiverse.com/search?q=quadruped&sa=I do not have the robot with me, so I do not know the dimensions.
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