Looks nice from where I'm sitting!
The digital probe you recently purchased will quickly become your most valuable cooking tool...keep it in a dry place where it won't be damaged, and use it regularly. It will reward you with many great smoked meats.
If it was a bit dry, yes, it was overcooked, as you already know. 165* in the breast and 170* in the thighs for me...plenty of juices and safely cooked to >/= minimum safe recommended temps (165*). I go a bit higher in the dark meat for personal assurance, and the dark meat is more forgiving with temps than white meat, regarding moisture content.
Also, it may have been a bit heavy on smoke wood volume (I'd probably use half the amount of chunks), but the species can have a huge impact on flavor as well. I like apple, cherry and pecan with poultry (or any combination of the three is excellent). Mesquite and hickory can be a bit strong for birds, but are a good pairing for stronger flavored meats such as pork butts and brisket, and many other cuts of beef. Keep in mind that heavier (mesquite) and sharper (hickory) flavors from smoke woods are less forgiving than the fruit/nut woods, so I'd use them sparingly, at least until you have a good work-up for a long, thin smoke.
Your mention of butter is a good start for a more crisp skin, which is very difficult to achieve cooking low and slow. If you'd like a crispier skin, one of the easiest methods is to pull the bird about 8-10* before finished and toss into a 400* oven or indirect heated gas grill. Finish cooking to desired temp. You won't miss any smoke flavor during this stage, as once the meat hits 140* or so, smoke reaction/penetration generally has stopped.
Don't go by the temp gauge on the the lid for chamber temps (useless, except as a general reference). Puting your probe on the grate just below the food is the best actually temp indication. Drill a 3/16" hole through the barrel to insert the probe through the side a coupl einches below grate-level is the easiest with the gourmet.
Oh, one last thing: the lowest grate (rests on the rim of the water pan) is more for steaming, and will get less smoke and less heat to the food. The upper grate runs hotter and a bit less humid. The upper grate position will also aid in a crispier skin on your birds.
You're well on your way to a future of great smokes!