Pulled pork for large group

I rarely do a butt in a crockpot, but they will take them to the magic 190-200 degrees for pulling. I would suggest that rather then trying to use liquid smoke and rub you use a smoky BBQ sauce you like. Go light on it, 1/2 cup probably for 4 or 5 hours, drain and then add another 1/2 cup for the finish. After you pull it you can add more sauce if it's needed.
Set on low you can't overcook a 7 or 8# butt.
I agree that about 1# raw meat per adult should be about right.