Injection is not necessary for moist brisket, proper cooking of the brisket is. I inject my comp briskets with a commercial injection mixed with beef broth to amp up the flavor for judges who are tasting 1 bite of your food, but at home I don't. The collagens breaking down properly inside the mat is the secret to a moist brisket along with a proper rest.
Fat side up, fat side down, this will be debated until briskets are extinct, you will just have to experiment and see what works best with your smoker and or pit.
Cook using IT as a guideline only. The real test for when a brisket is done is the probe test. IT guidelines include somewhere around 160-165, this is when if you choose to wrap you should do so. If you choose not to, at the very least place the meat in an uncovered foil pan to allow you to catch all the juices that will leave the meat once it is in the stall. The next IT guideline is around 190-195, this is when you should start probing your brisket for tenderness. About every 30 to 45 minutes after you reach 190-195, start probing the brisket in several spots with either a toothpick or your therm probe, once the probe slides in like a hot knife through butter, the brisket is done. Pull the meat from the pit, allow the IT to drop to about 180 or so, then off to a cooler for the rest, normally 1 to 2 hours, but you can rest for longer if needed. The optimal IT for slicing and ultimate moisture and color retention is around 160-165.