There is no reason you can't start the big butt as planned put a couple hours of smoke on it then add the little one latter and add more smoke wood.
Here are some things to consider...You are smoking for a party, CYA and figure at least 2 hours per pound at 225° and add 2 hours just in case you get a stubborn butt or something goes wrong. If you are done early, double wrap in foil and towels and place the meat in a cooler where it will easily stay hot for 5-6 hours with that much meat. Next Pork Butts only get smoke on the outside. They are then pulled and the smokey surface bark is mixed with LOTS of meat that has no smoke flavor. Point is, in the case of Butts for Pulled Pork, there is no such thing as too much smoke and Apple is one of the mildest smoke woods out there. If all you plan to do is put 2 hours of smoke on that meat, you might as well Oven Roast it and sleep in. Many of us add smoke to butts for 10 hours or more. The Stick Burners add smoke the entire cook!
As far as the water pan goes, some use it some don't and many use it only in the beginning of the smoke. Read this article...
http://www.smokingmeatforums.com/a/wet-to-dry-no-foil-smoke-chamber-method-for-smoking-meats
Many of us take the flavor a step further and add a Finishing Sauce to the Pulled Pork. Below are two of my recipes that are super popular around here. The Tangy one is most popular in the Southern States but I'll throw in the Sweet one, good for Ribs too, in case that is a flavor profile you think your guests will enjoy...JJ
Tangy Pulled Pork Finishing Sauce
This is more of an Eastern North Carolina style Finishing Sauce...
2 C Apple Cider Vinegar
2T Worcestershire Sauce or more to taste
1/4C Brown Sugar
1T Smoked Paprika
2 tsp Granulated Garlic
2 tsp Granulated Onion
2 tsp Fine Grind Black Pepper
1 tsp Celery Salt
1 tsp Cayenne Pepper or Red Pepper Flake. Add more if you like Heat.
1/2 tsp Grnd Allspice
Combine all and whisk well. This is a thin sauce, bring just to a simmer and remove from heat. Adjust sweetness by adding Brn Sugar or additional Vinegar as desired...Makes about 2 Cups.
For a
Lexington Style Dip add, 1/2C Ketchup and 1-3tsp Red Pepper Flakes...
Foiling Juice / Sweet Pulled Pork Finishing Sauce
Foiling Juice
For each Rack of Ribs Combine:
1T Pork Rub, yours
1/2 Stick Butter
1/2C Cane Syrup... Dark Corn Syrup...or Honey
1/4C Apple Cider...or Juice
1T Molasses
Optional:
2T Vinegar, 2T Mustard and 1/4C Ketchup to make it more of a KC Style Glaze.
Simmer until a syrupy consistency.
Allow to cool for 5 minutes, pour over foiled Ribs and
run your 2 hour phase of 3-2-1. For the last phase return
the ribs to the smoker BUT reserve any Juice remaining
in the Foil. Simmer the Juice over med/low heat to reduce to a saucy thickness. Glaze the Ribs for presentation or service.
For a Sweet Finishing Sauce for Pulled Pork: Make a Double batch, Butter optional.
Add 1/2 the batch to the Foil Pack or place it in a Pan with your Butt, if you plan to do so, when the IT hits 165*F.
Cover the pan with foil and continue to heat to 205*F for pulling.
At 205* rest or hold the Butt in a cooler wrapped in towels until ready to serve.
Pull the Pork and place it back in the pan with the pan Juices and any additional reserved Foiling Juice to moisten and Serve...OR... Bag and refrigerate until needed.
When re-heating place the Pulled Pork in a Pan or Crock pot and add reserved Foiling Juice or Apple Cider, as needed to make up the Juice that was absorbed while the pork was refrigerated. Cover and re-heat in a pre-heated 325-350*F oven or on High in the crock pot to 165*F and Serve.
Note: the addition of the reserved Foiling Juice or Apple Cider should make the PP moist but not Swimming.
I was AMAZED...No additional sauce needed. ENJOY...JJ