Dance Group Lighting Question

[PixNW]

Most of my photo biz has been shooting sports action and doing individual and team images and custom posters.

A friend of my daughters is in a dance group, and her mom is familiar with my sports work. They have asked me to shoot the group and individual pictures for the dance group. I have been thinking about starting to do this kind of work as I have been asked to do photos for a large football league next year. The dance group will be photographed indoors at their studio, which doesn't have great lighting. I will go by this week and see what I get metering it with my camera. The groups will vary in size from 8-17 girls, plus the individual shots.

I will be using a 1D Mk IIN, probably with amy 24-70 2.8L. My only light right now is a 580EXII, and I have a Gary Fong Whale Tail for it as well. I know that I will probably need more light for the group shots. I am tempted to order another 580, and maybe an ST-E2. I like the idea of being totally wireless without having to use trans/recvr's, and being able to adjust from the camera. Would I be better off ordering a couple of Alien Bees? I know I could get their portable power pack for shooting outdoor football team photo's where no power is available next year. Still, if they could be adequate, using 580's has quite a bit of appeal for me. For the dance group, would another 580 fired into an umbrella be adequate, and use the on camera 580 for some fill?

Any thoughts and advice would be most appreciated. The shoot is the middle of next month and I want to get whatever I need ordered so that I have some time to experiment with it a bit.

ON EDIT: After doing some more reading I am thinking that a good setup may be to get another 580EX to use as a slave. For the group shots shoot it into an umbrella placed about 45deg from the group, and use the on camera flash for some fill, with the power being about 3 for the off camera to 1 on the camera. Does that sound reasonable? My thinking is that for the individual shots I could probably not use the off camera flash and use the Whale Tale on camera as it provides fairly soft light for individuals. Thoughts, advice?

[PixNW]

Anyone? Any thoughts or advice would really be appreciated.

I think what I am going to do is order an Alien Bee 800 along with one of their newer 64" parabolic diffusers, with a black covering for the back so that it can be installed as used as a reflector, or taken off and used as a shoot through. I'll put it on a 13' lightstand. I will also order a set of their wireless battery powered receivers and a trigger. I think I'll use the AB800 cetered behind the camera, and higher than the group. I can use my 580EX II down low and in front of the group, but out of the shot, for some fill, also fired with one of the AB receivers. I've looked at some images that were shot with a setup like this, and for group pics it seemed to work pretty well. I think it avoids some of the issues of shadows and unven lighting that some other methods can produce. The 800 should hopefully have enough power to evenly illuminate the small groups pretty well. Before next football season, when I'll have to do football team pics without power available I can get a Voyager portable power system.

Any advice is very much welcome.