I'm not a caterer, restaurant owner, or chef. I'm just a guy who knows how to cook and often provides smoked food for parties, potlucks, family get togethers, etc. Allow me to brainstorm this with you.
First, I'm not sure why you want to provide both pulled pork and pulled chicken. If the pulled chicken is going to be served enchilada style, I get it. If it is going to be serve with the same BBQ sauce choices, I'd do one or the other but not both. Pork is easy, inexpensive, and you don't have the bone choking hazard you'd have if you smoked whole chickens and pulled them. Boneless, skinless chicken breasts and thighs are just as easy as pork, much quicker to smoke, but generally slightly more expensive. Both pork and chicken are fairly neutral meats, but pork just has better flavor IMO. Just a thought.
Concerning your idea about serving unsauced meat and a variety of sauces, three things come to mine. First I've found it is best if people at parties and potlucks don't have to make decisions about how to prepare their food once it is on their plate. The line moves faster because there are some people who literally can't make decisions, especially about food prep. Plus, you lose control over the flavor of your offering. Second, sauced meat, even lightly sauced, will stay moist and juicy longer than dry meat. Third, I love Chef JJ's finishing sauce. I don't serve pulled pork without it. I've taken squirt bottles of Chef JJ's finishing sauce to three parties/potlucks, instructed people how to use it, and still came back with almost full bottles. Now I just put it in the meat before I serve it, which kind of circles back to the first point.
My recommendation would be pulled pork or pulled chicken only, lightly sauced for moistness. I've never taken pulled chicken to a party or pot luck, only pulled pork. If you are the sole supplier of protein, 20 lbs of bone-in pork butt/shoulder will be plenty. If there are going to be other folks bringing burgers, hot dogs, sausages, ham, etc, half that amount. If you don't want leftovers tell folks to take home what's left. It will all disappear.
There are lots of rubs you can use that are neutral. My favorite store bought is McCormick Sweet and Smoky. It works on pork or chicken. Best price is at Wal-Mart. I don't think I could make it for their sell price. I can post my recipe for the same thing here if you want.
Finally, it sounds like everyone else is going to be bringing sides. If you want to contribute in that area, use the search feature above for Dutch's Wicked Baked Beans. It can be prepared without the peppers and is still delicious.