Kevin, you're going to love the WSM. I might suggest that you buy a Brinkman CHARCOAL pan. It fits the WSM waterpan brackets perfectly, and will give you double the watersupply. It's about $3 or $4 at Academy Sports and Outdoors stores.
I've tried many different combinations for heat-sink purposes in my WSMs. Sand didn't really do it for me, since if I'm going to fire up a cooker I'm going to fill it up, and the heat radiating off the sand did unforgiveable things to the meat on the bottom. The clay flowerpot base that I tried cracked during the first cooking session, and I never took the trouble to get another one.
I've settled in on two methods at this point that suit me best - if I'm cooking hot (which tends to be most everything except butts anymore), I use the stock waterpan with two layers of foil on it. If I'm cooking at traditional temps, I go back to the Brinkman charcoal pan with water. Somehow I just like what it does for the meat better than any other option I've tried.
As far as that big brisket, one thing that really works well is just to cut a hunk off the point end of the brisket, rub it, and lay it on the rack next to the rest of the brisket. That chunk is my favorite part - it'll cook and render up to a very tasty hunk of "burnt ends". Also, when doing a packer on the WSM, save the big chunks of hard fat while you're trimming it. When you lay the brisket on the rack, tuck that fat underneath the ends of the brisket. That way, the ends of the brisket will be better protected from the harsher heat that comes up around the edges of the waterpan and up the side walls of the cooker. Works great.
Take a look at the "as-seen-on-TV" Ove-Gloves as part of your glove arsenal - I think they're at most Walmarts, Walgreens, etc. It they get wet they're useless against heat, but as long as they stay dry I can pick up a WSM base that's full of burning lump with them and never feel the heat - even pick up the charcoal grate still burning. (We've added handles to the charcoal grates). I've been using the sames ones for close to three years now, washing them almost every week, and I'm still amazed at their effectiveness.
Enjoy! Keri C