Yes, you'll need to cut down the size as it definitely won't fit the MES. Total cooking time @ 225* chamber temp would be around 1.5 hrs/lb, depending on elevation, etc. Cutting in half, leaving the bulk of the flat on one piece and bulk of the point on the other, will reduce cooking time for the point somewhat, but not alot. You could push about 240* and reduce the cooking about 15-20%...at the cost of a bit less smoke flavor.
Mopping: every time you open the smoke chamber you lose heat and smoke...this requires additional time for recovery of temps and regain what you lost. I don't mop, just me, but I do prefer the lower 225-235* smoke chamber temps.
Injecting: I don't recommend it due to turning an intact whole muscle meat into a compromised muscle which is recommended to pass through the 40-140* internal temp range in 4 hours...commonly referred to as the 40-140/4hr rule, as described here:
http://www.smokingmeatforums.com/f/181/food-safety
Juiciness of a brisket doesn't seem to be effected that much by injection. Sure you can add to the flavor profile with things that you wouldn't normally want to use in a dry rub, however, if you consider using beef broth as a base for your injection, could you not use beef bullion in your dry rub? Anyway, think about this: the same hole you make with the needle to put the liquid marinade/broth into the meat is the first place the liquid wants to go back out when the meat begins heating up and the muscle fibers start to shrink from cooking. Think of liquid in cooking meats like electricity...it follows the path of least resistance. If the muscle has not been injected, the juices have to spend more time looking for a way to get out...translated as: more juices in the meat when cooked low & slow after reaching finished temp. A muscle full of holes placed into a hot cooker offers little resistance for escaping juices...they find a way out faster, thus less left over when the meat reaches finished temp. Smoke chamber humidity has an effect on this as well...drier means more retained juices due to tightening of the surface fibers of the meat. This is more noticeable with lean-trimmed meats.
Read this when you get some time, but don't worry about it on your first time with a brisket...you can see/eat your results, then discover what you like or didn't like about the outcome, and work on things to make it a little better (we can help you work these things out once you know what you like/dislike based on your result), as every smoker and everyone's preferences will vary.
Wet-to-Dry Smoke Chamber Method
This thread gets right to the chase on brisket with wet-to-dry method:
http://www.smokingmeatforums.com/t/141647/brisket-with-wet-to-dry-smoke-chamber-q-view-method
And, a satisfied follower who used wet-to-dry for a brisket flat:
http://www.smokingmeatforums.com/t/140362/another-brisket-forluvofsmoke-erics-method
Fat-cap up or down: I go up, to allow the fat to self-baste the meat as it slowly renders down during cooking.
Finished internal temp: the higher you take the I/T the more tender it should become, but this also increases the risk of a drier finished product. 185* should produce a fairly tender slice...closer to the 195-200* mark will yield a pull-able meat...not easily sliced thin, and can be difficult to slice thick as well. Be sure to probe for tenderness before removing from the smoker to rest...if it probes with slight resistance, it's slicing-tender. If little resistance is felt, it's pull-tender.
Hope this gives you some food for thought and some additional starting points to plan around.
Many will say that brisket is a beast to smoke and smoke well (tender & juicy)...don't fear the brisket...treat it with it's due respect, learn from this (and every) smoke, and continue forward, bringing what you learned to each smoke that follows.
Eric
