The fat cap is still a disputed area, like vent settings or water pans. One groups says fat cap up so that the brisket slowly biases itself while cooking. The other uses the fat as a protective coating so that the flames in a fireburner can't quite get the meat, me I tend to go with the first train of thought.
While I have not injected a brisket, I have marinated many times but usually when I am oven cooking (yes it does happen and more than I would like). So what I am saying is, when smoking I don't go in for those type flavor enhancements. Although many do, especially the injection usually of beef broth with maybe some lea & Perrins.
You know me, its a rub of salt, pepper, and a little garlic and some onion if I am getting wild......LOL
220 degrees to about 190 to 210 IT, use the toothpick method to check for doneness..... believe me you'll know. Then bag it, tag it (maybe some finishing sauce, maybe with some boiled marinade) and in the reefer for at least an hour. Why? Cause if it doesn't cool down some, it a bugger to cut, AND always cut against the grain. Berry berry important.
Most folks here use the crutch method, just like the butt, they foil it. In which case about 175 IT foil it with some foiling juices and return to the smoker to about 190 IT, then bag and tag and let set to approx. 205 IT (that's 2 or 3 hours, I still recommend the toothpick)
I have never needed it personally, but have saved friends briskets when too much beer was consumed while cooking, if the brisket is dry you can pull your fat out the fire by mixing some of that boiled marinade with some beef broth (or even then nasty beer stuff that got you in trouble), add the brisket and the broth in a foiled pan and allow to steam a few in the oven. Like I said, I never needed it personally.
This is a long smoke, well it is at my house! You can use any wood especially the hard smokes, mesquite and hickory. Mesquite would be the traditional smoke I assume but me, I still fall right in line with pecan... I just can't help myself, I don't know why I even try the other woods.
Remember the key word here especially is "Patience" It will be rewarded!