There are many brisket recipes and methods out there, finding the one that works for you is the key. But of course being your first one, feeding a crowd, you really don't have any time for experimentation, so below I have posted my method, works well, you can slice, pull, or chop the brisket after this method. As far as rub, just about anything wil work on a brisket, the cut is so large that the rub is a minor part of the flavor alongside the smoke, the beef should be the stand out flavor, the star of the show. If you have a seasoning that is popular in South Africa, maybe a steak or beef seasoning, that will work just fine. You could also use any of the rubs you can find here on SMF as well. Best of luck to you and your smoking adventure!
225-250 pit temp, smoke for 4 to 6 hours until the IT reaches 160 or so. Fat side up or down, your preference, but if your heat source is below the meat, go fat side down to protect the meat from direct heat which defeats the purpose of smoking meat. Wrap in foil or butcher paper your choice once the IT has reached 160 (if your not a wrap guy, at the very least pan it at this point to catch and save the precious juices that will begin to come from the meat as it enters the stall, these juices will come in handy later for vac sealing leftovers or if your brisket turns out dry), continue the cook until the meat reaches 190 IT, at this point start probing the flat section (thin, lean end) every 30 minutes or 5 degrees of IT increase, until a toothpick or probe can be slid in easily, like probing a tub of butter. Once you have reached this point, pull the brisket from the pit, vent the foil or other wrap for about 10 to 15 minutes to allow the cooking to stop and the excess steam to escape, wrap in foil or foil pan if it is not already, place in a cooler wrapped in towels for at least an hour, 2 or more is better. Once the IT of the meat has dropped down to 160 or below (optimal temp for the juices to have been redistributed through the meat), it is time to slice it and enjoy. If your slices tend to be a bit dry, simply dip in the au jus or place the slices in a pan and drizzle the au jus over the slices, this will both enhance the flavor and assist with the moisture.
Have fun and most all have patience!
A simple Texas style rub to try: 4 parts kosher salt, coarse black pepper, brown or turbinado sugar, then accent with 1 part each onion powder or flakes, granulated garlic, then ½ part each of cumin, chili powder and cayenne.