I have heard and read about "resting" the meat. At what point during the 3-2-1 method should I do this and for how long?
Steve resting would be after the 1 if you do the 3-2-1. The rest enables the meat, to take juices back in that, would run out if you cut right into it.
My ribs "rest" for about 5 minutes or so between the time they come off the pit until I cut them up. Doesn't affect quality of the ribs a bit. YMMV.