Rubs are a religious decision. There are lots to choose from, and most are about as good as any other. The key is to avoid black pepper, since that will burn and produce a nasty taste over the hours required to cook a brisket. Many people rub the night before -- frankly, since the meat spends several hours cooking I don't see the point. I usually rub the briskette right before I start the fire. Let it sit at room temperature until the fire is perfect (this can take some time if you're doing it right), and then put it on the fire. You want to avoid shocking the meat by going from 40 degrees to a hot fire, so let it pass briefly through the danger zone on its way to the fire. No bad critters are going to survive several hours of 225 anyway.
The fire is critical. Use a chimney starter. The taste of lighter fluid is not what you're looking for. A brisket will stand up to a lot of strong smoke, so I use hickory or mesquite if a fruit wood isn't available. Some of my best briskets have been smoked with the pear wood from a friend's tree that fell over in a storm. Come to think of it, there's a cherry tree in my yard that might be a hazard and will require some chainsaw work....Just make sure you've got all smoke and no flame. Flames produce creosote, which isn't very tasty.
Many people wrap their brisket in foil for the length of the cook. Yes, that will keep the juices in when the fire is too hot, but it's not barbeque. Barbeque requires smoke, and armoring the brisket so that no air can get in and the steam can't escape keeps the smoke away. Yes, it will come out tender, but you'd get better results in a crock pot with some liquid smoke.
There is a lot of controversy over whether to put the fat side down or up. Proponents of fat side down claim that it keeps the brisket from drying out. If your brisket is drying out, the fire is probably too hot. I put the fat side up with a chamber temperature of 225. As the fat renders it bastes the meat. If the fat side is down, it bastes nothing. The flavoring you put on the fat side travels through the meat nicely.
Mopping depends upon the flavor I'm going for. A nice chili encrusted brisket can be done without a mop sauce. But if you're looking for a more traditional barbeque flavor a good thick mopping sauce is a wonderful thing. Just stay without something thick enough to not run right off the brisket as soon as you mop it, and it should be able to stand up to the heat -- so nothing sweet at the sugar/honey/corn syrup will burn. Once an hour seems to be the magic number, but you mop it as much as it's needed.
How long to cook? How many hours per pound? Sorry, no answers. You must cook it until it is done. You should be able to stick a grill fork into it and twist easily. The internal temp should reach 180, but you'll still have some time to go until it passes the twist test. If your brisket has a tip that finishes first, cut it off and set aside. You can use this for a great sandwich while you're waiting for the rest of the brisket to finish.
When it's done (or very nearly done because carry over will be operating), mop it one last time, take it off the smoker, and wrap tightly in foil. Let it sit for at least an hour to cool down and let the juices redistribute. If it's going to be hours until the festivities start, put it into a crock pot with some of the sauce in the bottom and the heat at very low. This will keep it out of the danger zone for contamination without drying it out. I've cooked briskets the day before and left them in the crock pot until the next afternoon, and if anything they taste even better the next day.
Cut the brisket against the grain in slices thick enough for them not to fall apart. Many people chop their briskets and mix with sauce, but I think that's just an attempt to cover up tough and flavorless meat. You'll see that method employed in assembly line restaurants. They've got a lot of people to feed and they're not looking for perfection.
Serve on a plate or with a bun. And since I'm in North Carolina, I'll plop a nice helping of cole slaw on a sandwich or on the plate.
Enjoy. Even a mediocre outcome from a brisket that gets this treatment will be better than the better restaurants.