My 2 cents.. I would use my SB800 into a 24" umbrella mounted about 2 feet above and left of my head. Then a few test shots 1/125th sec or 1/60th so as to find the ambient light, and finally fill the folks with the umbrella light, adjusting the fill so as to be about 1/2 stop less than complete. This, I think is what TTJ is suggesting, I like the soft umbrella better. This attaches to me via a shoulder bracket and usually duck tape. Or, the Lumiquest soft box II, about 6" X 8" on the camera is fine with the fill about 1/2 stop to one stop less than the overall. Lots of batteries and such. Gaffer's tape or duck tape will hold the soft box in the wind.
If the money is good enough, setting up a special shooting area with about three umbrellas, 1200 WS or more of strobes, powered by a generator or such from a pickup truck...or RV. Maybe even using the bands tour bus, if it has a logo on it, for backdrop...
I might think about some real crowd control, and having a good assistant to direct the folks exactly where you want them. Low angle or high angle shots are interesting in some of these, but I do not know what the end use is.
One other point, shooting at reduced power, 1/4, 1/8 should give a rapid recycle and allow at least a couple of shots per "group". I will say "On three" and then shoot on two so as to avoid blinks.
Oh, well... good luck!