Hi, Al. I've cooked a brisket or two over the years so I'll help you out with that part of your question.
It sounds like you are cooking a brisket flat as opposed to a whole brisket, also called a "packer" brisket. I'm arriving at that conclusion based on your statement that it weighs 6 lbs. I think a packer, meaning that both the flat muscle and the point muscle are both present, would weigh at least a few pounds more. Anyway, cooking at 250°F, using Blue K and cherry is a good place to start. You'll want to season your brisket and then place it on the top grate of your cooker. You won't need to do much except monitor the cooker temperature for the next 4-5 hours so you'll have some time to ponder your next move, that being "to wrap or not to wrap".
While it is traditional to cook a brisket to doneness unwrapped, may people, including most competitive cooks, will tightly wrap their briskets in foil at some point along the way. If you decide not to wrap, all you really need to do is start testing the brisket for doneness as nears the end of the cook. Most people typically perform that test by inserting a probe into the brisket from the side, across the grain and feeling for any resistance. If the probe glides in and out of the meat feeling like it is as soft as warm butter, the brisket is done. At that point, take it off the cooker and wrap it tightly in foil for the rest period. After wrapping in foil, many people then wrap it again in an old towel and then place it into a dry cooler for at least an hour. This will give the meat a chance to relax as it cools slightly and I do mean "slightly". It will still be very hot when you are ready to slice it up so don't worry about it entering the food danger zone.
If you decide to wrap, you'll want to do so when the internal temperature of the brisket is at about 165°F. Wrap it tightly and then return it to the cooker to finish. It will cook faster in foil so be sure to check on it after about 60-90 minutes. (I mean do the probe test I described above.) Once it is done, open the foil and let it vent for about 5 minutes and then close up the foil again and rest it as previously described. There is likely to be some hot liquid in the foil so be careful and don't let it leak out.
I hope that helps you out a bit. Have fun and enjoy your WSM!
