First of all hello and welcome.
Secondly if the smoker is brand new I would not smoke briskets in it first. Instead I would get a nice FATTY pork butt that weighs like 8-12 pounds and smoke that 2 days before your shindig. Follow Smokin's 101s on a pork butt - really criss cross cut the fat cap, apply a lot of rub everywhere, place it in the smoker fatty side down (if yoru shindig is Saturday smoke the pork butt Thursday night over night. Yup, it is as easy as that. 225 degrees for 12 hours. 2 oz of wood, no more. In the morning your yard will smell like paradise. Let it cool wrap in double foil in a 13x9 pan and refrigerate.
NOW you have started putting a little cure in your smoker. Doing a couple of briskets the first smoke is doing the difficult stuff first. Pork butts are a snap.
OK so now it's the day before your shindig. Take out TWO of your briskets (not three !!), wrap and freeze the 3rd one for another time. I tell you this because the specs on the SM025 say 20-25 pounds. I've tried maxing out my SM008 a couple times and it took forever to cook. IF you do a pork butt one day and two briskets the next you'll have lots of tasty food. You get a more accurate and quicker cook with 2 8-10 pound briskets, trust me I made that mistake too. LOL
Now apply a rub to them. Let them sit for about an hour with that rub on them so the insides warm up some. Then into your smoker about 8pm at 225 for 12 hours. Like with pork butts I find that is a good cooking time/temp even for a smaller pork butt or brisket. Same deal 2 oz of wood, no more. Believe me meat that had too much wood is not so great (speaking from experience). LOL. Have a couple adult beverages and go to bed.
Ok it's Saturday the day of your shindig. You get up get some coffee and go check on your smoker. With a quick read digital thermometer you probe and test for temperature all over your briskets. You want an internal temp of between 195 and 200. And when you slide in the probe it should go in easy like it's melted butter. Remove to a sheet pan and cover with foil 1/2 hour. Now separate the flat from the point, if your meat is truly done it'll pull away easy. Wrap the flat in double foil and then into a towel into a cooler. Apply more rub to those points and back in they go for about 2 more hours at 225 and you get burnt ends. Like this... When you got the burnt ends done put them in a 13x9 pan with a tiny bit of sauce, cover with foil and hold (you could use your turned off smoker for a holding oven, I do...
So now grab a shower and get the game tuned in. Read and re-read Smokin's 101s. SEARCH here for what the other excellent cooks do and get a feel for what you want to do.
You're doing things I'd never do. Making your first cook brisket and doing it for company. Me, I'd take that 3rd brisket and AFTER smoking a pork butt to season up your smoker smoke the brisket next, do it with just you and the family as the ginuea pigs. Then you'll have properly broken in your smoker and you won't be going into uncharted waters for company. Believe me after you've done a half dozen or so you'll be the baddest (meaning the best) in your area. No fooling.
Here's a video on burnt ends, check out his technique for brisket rub, cooking and separating the two pieces and burnt ends, it's this easy:
http://www.youtube.com/watch?v=zw8p4dpX3SUand here's Smokin's 101s:
http://www.cookshack.com/store...kin-Okies-101-Series