Hey Nathan. This thread looked lonely, so I'll help you out...
You need to decide if you are going to vend pieces, a half or whole bird and buy accordingly. If you are doing a half or whole, spatchcock (see youtube below) your bird, sprinkle the rub and throw it on the smoker. Brining definitely brings more moisture into the bird, but don't brine too long. Maybe 2-4 hours tops. The problem with brining is finding where to do it with a large amount of chickens.
Chicken is the most feared of meats, cause there is a fine line between overcooked and bloody. It just takes practice.
YouTube - How to spatchcock a chicken
The guy in the video cuts it in half after taking out backbone. Most people leave the keel bone in and leave the bird one piece. That is a classic spatchcock. This was the best video I could find. I would recommend stopping after you take the backbone out and spread the cavity. I like to take the ribs out as well, but that is up to you. Figure out your own style.
As to what you should vend, hopefully someone else will chime in. I do know that most of the public prefers white meat. I'm a thigh guy myself. Whole chickens are definitely cheap. You could do wholes and then offer the leg and thigh or the breast. You could then offer that half or whole on your menu.
As to holding, you can smoke to temp and then wrap in foil in a hold box or cooler until serving. Just make sure the temp is right when you serve. It tastes best right off the smoker, as the skin is crispiest. Once you hold it for a while, the skin will soften. If you are vending over a whole day, you could just stagger your birds throughout the day.
Below is a good link from Weber that goes through holding of cooked meat.
Hope this answer some of your questions.
Have a good one.