I made an Instructables here : http://www.instructables.com/id/EEZYbotARM/
In all joint I use M4 screws with round head
For the vertical arm I prefer to guarantee a better precision using two brass pipes. the lower one stay in position kept by the servos, the upper one is crossed by a M3 screw (I'll post a better explaining image)
First tests has been made with cheap servo sg90
than I changed the more stressed with metal gear servos MG90
only for the claw I left the plastic one (but this can be of your choice)
For driving the bot I made a lot of experiment using all the available method with arduino : sketches, potentiometers, joystick, WII nunchuck …. but at the end I discover a nice controller from Pololu that solves all the problem related to the servo driving in the easiest way. You can attach up to 6 – 12 – 24 servos depend of the controller type and it is provided with a software that give you the power to drive the servo in manual moving slides in the mean time you are able to set the values of speed and acceleration for any singular item. You can also build sequences of commands in a easy way, store them in the controller o get the code automatically. GREAT !
here the link of the Pololu servo controller