The UNO is the best board to start with.
How big is this robot? An UNO board is probably too large to fit where you want it. There's lots of smaller variants, such as the Micro and Nano. These are good because they have a USB connection for programming. The even smaller ones like the Mini and Pro Mini don't have USB so they need an FTDI to program them.
I am building a robotic arm of about 80 cm in length. Does UNO support dynamixel RX-64?
The purpose of the robot is to be able to rotate at least 180 degrees with about 5-6Nm of stall torque.
Would it be advisable if I use other basic servo motor ? (prefer servo as it is easier to config speed with pwm)
Perhaps Micro or Nano can be a good choice for my application.
May I know how does USB connection work for programming? (do you mean by simply plugging USB port to my laptop and program the board from there on?)