Welcome to SMF from Gilbert, AZ! You usually want to smoke butts until they reach a internal temperature of around 203º and are probe tender, then wrap them up and let them rest in a cooler for at least and hour before pulling the meat. I'd try to get butts that all weighed pretty close the same, say 8 pounds each. Give the butts a thin coat of some cheap yellow mustard so any rub you want to apply will adhere, you won't taste the mustard when the butts are done. I've got no idea what your smoker looks like or how it works. I'd spin them at 275º for about 12 hours using lump charcoal and hickory wood, spray them down with a 50-50 mixture of apple cider vinegar and water every 45 minutes to and hour. That ought to get you close to where you want to be. Doing 20 butts you just might want to find someone with a bit of pit experience to help you out. RAY