Don't over think it.
If cooking 4 shoulders, you'll want to load up as much charcoal as the chamber will hold.
Make sure you light up enough coals to start -- 1/2 to 3/4 chimney. When using the Billows, too much lit really isn't an issue (the limited airflow and the fan staying off takes care of the overshoots). But too little lit can be a problem. When the fan does blow to raise the temp, the air needs to hit enough glowing coals for the fire to perk up quickly.
No need for a horseshoe or any kind of fancy fire build. If your temps start to fluctuate a bit after 8-12 hours, you probably need to stir the coals and knock off some ash. FWIW, I usually rake the remaining coals into a pile close to where the fan is blowing.
