1) when I make pulled porkmy temp is 225 and14 to 16hrs. Your internal should be at 180 to 185. Then let it rest about 15 mins. I use an electric thermonitor itmakes it alot easier and you don't have to keep opening the door loseing the heat and smoke
2) Notsure but maybeto stop the meat from cooking.
here's one I did awhile ago took 16hrs but worth every minute
as for brisket times are a little longer and temps are about the same.
It's all trial an error, being each cooker is differant. Over cooking is some what impossible with the brisket & pulled pork. Not saying it can't be done, but you'd have to try awfully hard.