Watch all the PBS videos from Franklin (both prep and cook).
https://www.pbs.org/video/bbq-franklin-brisket-part-1/
You will nee a dedicated temp probe that stays in the meat the entire cook.
Look for pink butcher paper now. Order on Amazon if you have to. Wrap it in when it hits ~165F
Realize now that the piece of meat will take 1-1.25 hours per pound to cook so your looking at a 10-13 hour cook PLUS a one hour rest for the meat.
I can't say enough about how important the rest is. It is a critical step and simply can not be omitted or rushed.
The meat is done when the meat is done. Sometimes its at 203F (quite often) sometimes 190F. When you probe it and it feels like melted butter (no resistance) it's done if its at least 180F internal.
Start your fire early enough in the morning to give yourself the time to cook it properly. That may mean getting the fire going at 5:00AM in this case.
Prepare the brisket the night before. It will take 45 mins to trim it properly and season/apply the rub. Place the meat in a tub or pan and cover with cling wrap and store in the fridge overnight. Take it out the first thing in the morning before starting your fire so it begins to warm up.
225F is the best temp for low and slow but 250F won't hurt it and will speed up the cook a bit. Try not to go higher.
Realize you will have to add charcoal more than likely during the cook so have a chimney on hand to get some more going before you lose your heat. Pick up some pecan and or apple chunks to give it the best smoke flavor possible. Mesquite is too strong IMHO.
If your using your Weber make sure to build the fire on one side and put the brisket on the other side. You may need to rotate the meat during the cook as it will cook faster on the heat side more than likely. If you have a heat deflector (ceramic) use it!
I spritz. About every hour or so. I use apple juice and apple cider vinegar mix 50/50. Helps keep moisture in if you don't have a pan for water. If you can squeeze a water pan in it will help keep humidity up and meat not to dry out.
Have plenty of beer on hand. You can't cook a good brisket without a lot of beer!
Don't worry if it doesn't turn out perfect. Chances are it will not. This is probably the hardest cut of meat to master and it takes lots of failures sometimes before you figure out what works the best for your BBQ setup.
Good luck!