I agree with the others, keep it simple then go from there. I prefer equal parts (5 tbsp of each) coarse Kosher salt, brown sugar and black pepper (your choice of either coarse or fine, I use table grind), from there you can add 2 tbsp each of garlic powder and onion powder, then a little (2 tsp each) cayenne, paprika and chili powder to give it a little kick at the end. I make my rub up the day before, then I'll run this mixture through a Ninja or a spice grinder the next day to blend the spices and break up any clumping from the brown sugar. Season it heavy, very liberally, this is a big cut of beef.
Personally I have never had a brisket finish to fork or probe tender at 190 IT, but it's a good benchmark to start checking the flat section for doneness with a toothpick every 5 degrees after (195, 200, 205, 210) I pull most of my competition briskets at 210 or above, and yes it is fall apart tender, but that is the way I like it. Give it a good 2 hour rest in a cooler or at the very least on a counter covered with towels. For optimum moisture retention, it's best to not slice the brisket until it's IT has dropped below 170. This is why the rest is so important, the muscles need the time to relax after being under pressure from the heat for so many hours, allowing the moisture that is towards the outer surface to move back towards the center of the piece of meat.
Best of luck and happy smoking, but most of all have plenty of patience with the brisket, try to not have a timeline with it! it's done, when it's done!