I'm a newbie, but since you asked for tips, I'm going to add my 2 cents. Don't use a rub, just use sea salt. A lot of sea salt, like pour it on so thick it's falling off. Then put it on the grill and cook for 4 hours like you'd planned with charcoal and pecan, then wrap in foil until you reach an IT of 205. After 2 or 3 hours it has absorbed about as much smoke flavor as you'd want anyway, so you can just bring it in the house and put it in the oven at 235 for the remainder of the cook. Don't add the juice from the foil back to the meat, it's juicy enough and the juice in the foil is too salty.
No, this isn't something I created on my own, I saw it on TV. I was watching a cooking show and they were visiting a BBQ restaurant. This was the method he used to cook his butts. I thought it was weird until he said he cooked 60-70 butts a day. If you can move 60-70 butts a day it's probably real good, or you're giving it away.
I tried it. What it does when it cooks like this is absorbs the salt into the meat evenly and it really isn't too salty. In fact it seemed to just bring out the flavor of the meat and smoke, which is what you're cooking a butt in the grill for anyway. And the 205 IT is what I did to make pulling the pork a breeze. I live in an area where BBQ pork restaurants are the most popular places to eat, and all of my guests and family said it was the best they'd ever had.
You can spice it up with all sorts of seasonings and make a pretty bark that will get mashed into the meat when you pull it, then you just have seasoned meat. Or, try it this way and enjoy the natural flavor of well-smoked pork.