[pwreef]

The drivers just hook up in parallel to the power supply. The more you connect, the higher current PS you will need. How high exactly, depends on what current your LEDs are consuming. In theory 84 *3W = 240, so you should be well under that PS limit.
You can mix and match. If you are going to dim them, there is no reason to get anything but the 1000mA version. The only danger is that if you loose your Arduino or other dimming input connection, the driver will go full current. If you have some LEDs that cannot handle that, they will probably fry.
Arduino Mega 2560 that I am using has 14 PWM outputs. That should cover all possible colors you want and more. The controller I am using is linked in the video. He tried to post on here, but got removed because he is collecting donations. Parts cost about $50 including the touchscreen, clock shield and the Mega board from e-bay.