Aaron, a 12 lb packer should fit in the #2 whole (I've done up to 14 lbs whole, so long as they're not too long). Don't separate the point and flat - that's what makes a packer cook so good! If it's a little long, when you put it in diagonally, just let the ends curl up on the back and door. It will shrink to fit in no time.
I have a lot of respect for Brian's brisket advice, as he smokes more of them in a day than most of us do in a year! However, since we don't do it for a living, and have a little time on our hands for prep, why not do a little to "enhance" the flavor profile? I use my pork butt brine, and it adds a lot of flavor and moisture to the finished brisket. I've smoked briskets with just a rub coating, before ever trying any injections or brining, and I personally prefer a little extra work for the added flavor. If I were doing 20 at a time? ...probably not so much!
Find what your level of commitment is, because you can't go wrong either way - simple or complex prep. Find what works for you, and the best way to do that is to try different methods.