Jason Dominy is a great resource for this, as he's planned quite a few in the Southeast...
I'm on my third (Jan 16th at 4pm in Olympia at the Batdorf & Bronson Roastery) and it's been a trial-and-error sort of thing. We've had a couple of different ideas about how they should work, but in each scenario the coffee was available the week before the event for practice. With so many different roasting styles out there, it would be unfair to assume folks could just grab 20 or so grams of a coffee and brew it well under pressure, especially if they only have experience with one roaster's coffee. There are definitely pros and cons to different approaches, so you'll have to consider everything as interdependent:
1st battle - 7 competitors, each assigned a letter. Since it was in our roastery lab there was plenty of hot water available, along with all of our manual brewing equipment if they didn't bring their own. We had three judges (one was a coffee professional, one a food professional and one a coffee enthusiast, to have a wide range of palates and preferences represented). 15 minutes for competitors to brew as many cups as they can (only one cup to be presented to the judge's table) with any brewing method they chose. Cups were placed, with assigned letters underneath, on the cupping table while judges were in the next room. Judges were called in and they took about 15 minutes to discuss the brews using a simplified tasting score sheet (very basic - 1-10 scores on Aroma, Flavor, Mouthfeel, and Overall Impression). The highest score wins. The thing we learned about this time was that the competitors and audience didn't know what to do while judging was going on, so it was pretty awkward to just stand there and wait.
2nd battle - This one was at our Espresso Bar in Olympia. Pretty much the same format, but slightly different judging panel (one was our green coffee buyer and one was Olympia Coffee Roasters' green buyer, while the third was chosen from the audience). Again, everyone had access to the coffee a week prior to the event. The judging process took about 20 minutes, and this time we had the competitors clean up and get the place looking spiffy again. There were more people at this event, so there was no "down" time while judging was going on, and socializing made the time go by.
The major lesson here for us was that judges need a time limit. Though they didn't take much longer to judge, it was when the place was clean and the socializing began to slow down that they noticed everyone was watching and waiting for a decision (it only took 30 seconds after that). If there was a predetermined time limit (with a timer, perhaps) they would have been more conscious of getting it done more quickly. Not that they were dallying, there was just a lot of second-guessing and debate. A time limit would have made that part go a little more quickly.
The third hasn't happened yet, but I'm hoping that the lessons from the first two make it more of an Event. We plan on live music and snacks to fill the time (brewing and judging). We'll see how it goes...
One concern I have: brewing devices versus very different brewing devices and how the flavor changes as it cools. In my experience, V60 brews benefit (flavor-wise) from cooling, whereas full immersion methods don't seem to hold up as well. And, perhaps through sheer coincidence, the V60 has won both of ours. In the Southeast battles, however, I don't think it's been the same.
The Seattle CoffeeFest Brew Ha Ha did a quick elimination round of V60 brews, in which competitors had to use a V60 to qualify for the next round (where they could choose a method, I believe). I wasn't there, so I can't vouch for how it was organized or the flow of events. You may wanna try to find a post on BX about it and see if you can't glean a few ideas from there.
I highly recommend them for the community-building aspect alone.
The only "manual brew battle" I've seen was at the La Marzocco Out of the Box in New York City. That "battle" had something to do with a certain coffee in your choice of brew methods that was then passed through the Extract Mojo and tasted.
Personally, I think the results were skewed towards the Mojo reading and away from the taste.
I think the better route is to make up your own rules for the battle. They'll probably be better than what's being used elsewhere - or at the very least: just as relevant.
We've toyed with the idea of having one here.
My thought is that it'd be best to try to have all of the coffees at the judges table at once... that way there's no luck of the draw, judges calibration issues, etc. Best cup wins. This also gives the judges the chance to do paired comparisons. Maybe you have thermal carafes available to keep things stable for the few minutes while everyone finishes?
Anyone else think it'd be a good idea to prepare a group of cupping sample for judges to use for calibration while the competitors prepare theirs?
I feel it's best to stagger your competitors instead of having them brew all at once, for the simple reason that the judges can evaluate each of the brews throughout their entire range of temps and flavors without the chaos of several, several brews in front of them.