Ron, two whole schools of thought for what temp to use for brisket and other meats. Your new WSM may cook at a higher temp than you want, this usually settles down after your cooker builds up a good layer of "gunk" on the inside, especially at the joints, being the rounds. If you have time and are so inclined read the thread on HH brisket. It is my way of choice but many will differ.
Most folks if they are going to foil do so at about 160. If you are able to maintain 225-250 figure about 1.5 hrs per lb. If HH cook about 2 hrs then foil then go till done, I give about 4-5 hrs. You can wrap in foil and then towels and in a cooler for several hours with no problem.
Good luck, if you let her cook till done you will be fine and have a great meal.
Mark