100lb pig is pretty small. After gutting, you're looking at about 70lbs which would yield about 30lbs of cooked meat. 30lbs of meat will make about 120 sandwiches.
A smaller pig means less fat. If you have the option, personally I'd cook the pig with the skin on. Since there's little fat, the skin would help to protect the meat from the heat. This would require the pig to be scalded to remove all the hair and to cleanse the skin.
Not sure of your pit size, but I like cooking with the head on. The tongue and cheeks are some of the best meat on a pig.
If you're cooking skin-on, you don't need to worry about a dry rub. You may consider an injection. I like to use injections that include a phosphate. This adds moisture. FAB, Kosmos, Make It Meaty, Butchers...they all work. I like Make It Meaty and Butchers injections.
If the pig is skinned, use a dry rub with little or no sugar. On a long cook the sugar will burn. Equal parts salt, course black pepper and granulated garlic works well. Also use the injection.
Again, not being able to see your pit I'm not sure if racing style is going to work for you. I just lay mine out on their belly. That said, if you can split the pig and cook it on it's back you have the option of using a mop sauce, which is good too. Takes a big cooker, though.
I cook my hogs at 265*. I'm typically always doing a 250+ pound hog and at that temperature it takes about 16 hours to reach 195* in the hams and shoulders. I would guess it would take a 100lb pig about 10 hours...??? Depends on your pit.
Don't allow your temps to get too high or you'll discolor or even char the outer layer of meat and it'll be like jerky. Here is one I got a little too toasty:
That pig I was cooking in a cooker like this. It's not really a pig cooker and more of a smoker, but we made due. It was a challenge to get an even cook with a large animal in there.
This is more of what you're looking for.