I have been asked by someone to provide an LED Dimming circuit. Currently there are 21 LEDs @ 1Watt (12V) each. The LEDs currently are just being switched on or off. Since I have not done anything like this at such wattage before, I would like to request some help in deciding how to drive them.

I am considering driving it using 16F877A. I will use HPWM output for this, but I would like to ask
  1. What frequency should be used?
  2. What should I use to drive the LEDs, a powerful Mosfet or something else is there in the market for this purpose?

I will keep updating my questions here as I will go along. If mosfets can be used then I would like to ask which one is recommended. Searching the internet I found some mosfets which are capable of 60Amp to 80Amp. Will these be a wise choice? Will heatsink be required?
Thanks