I'd fire up with two fully-lit heaping Weber chimneys-full-- this translates to filling the charcoal ring to the top. I say fully-lit because you are going to have over 20 lbs. of cold poultry in there sucking up heat energy, and this won't be an extended cook. Leave the water pan dry, and shoot for 325-350* cooking temp.
I always recommend brining turkey for best flavor and moistness. If you don't want to be bothered or don't have space to do that, just purchase enhanced birds.
Placement shouldn't matter, but I'd probably put the whole bird on top. As far as cooking faster, a turkey breast is just a turkey quadruple amputee, so a 10 lb. breast probably started out life as a 12-13 pound whole bird. If you also have a use for additional dark meat, why not consider just cooking a second bird-- turkey breasts cost usually much more per pound than whole birds.
You'll probably be looking at a little over 3 hours at 325-350, but as always, go by internal meat temp, not just time.
