I frequently buy wood from HD and Lowes, and generally have been pleased. I do have a bag now that I believe is old because it doesn't seem to impart any flavor to the meat. I need to get another bag.
As to your butt questions, this is really best for the general forum as I'm sure Smokin' will tell you, And a search would have answered your questions easily, but I'll be quick and throw out an answer.
As to size, I usually buy the largest 2-pak of butts they have at BJ's/Sam's/Costco. They usually are about 15# total weight or about 7.5# each butt.
Cooking temp would be 225-250*
Cook as long as it takes to reach 190* internal meat temp or higher. For pulling you'll likely want 195-200* internal temp. Let meat rest for an hour or so after cooking. I usually just turn smoker off and let it sit, sometimes for 2-3 hours. Meat will stay plenty hot, but will be easier to handle.
Rub is garlic salt, cayenne pepper and that's it for me. About a 9:1 ratio.
As to time, it's done when it's done. More meat seems to cook faster than less meat, so I always do 2 butts minimum at a time. I figure about 9 hours for 2 butts at 225*, but I don't open the door at all. The mystery of what happens inside my cooker while it's working is something for which I have little curiosity. I just let it do it's thing while I sleep.