Ok, that didn't come thru very well...not sure why I just didn't give you measurements.
The top wheel should be closed to about an 1/8" to 1/4" hole. The bottom damper should be closed to somewhere between 3/4" to 1".
The BGE holds temp very nicely. First mistake I made on my first pork shoulder was I didn't put enough charcoal in, so the fire went out about 2 hours prior to being done. Had to improvise - stick in charcoal down the sides which was a huge pain in the rear. Now I load it up...would rather have too much than not enough, I just use the coals for the next cooking.
Also, you'll find retailers will cut you a discount if you buy quantity of lump charcoal, several stores out here give 10% off if you buy 10 bags. The coals matter too, some create more sparks than others and some don't get as hot. There are decent reviews on charcoals here
http://www.nakedwhiz.com/lump.htm.