Night Flash Strategy

[acutshall]

I have a night outdoor reception coming up and need assistance with a flash strategy. My only experience has been studio strobes and portable flash set to manual with stationary subjects.

1st scenerio:

The ambient light if any will be low
The subjects will be mobile. i.e dancing.
I always shoot in manual mode, stationary subjects
I do not want to blind and irritate guests with flash, I want to limit to those whom I am shooting.2nd scenerio;

I need to take pictures of the band without using flash at all and need examples of exposure seetingsMy arsenal consists of the following;
2 QFlash 5
3 580exII
1 assistant
1DMarkIII
Camera bracketOne thing I have considered is to mount a flash (set to manual), to the camera bracket and use for fill. Have an assistant with qflash(PW)( set to manual) mounted to lightstand located behind or at a 45 degree to subject. Both keeping at a predefined distance to maintain exposure.

For convenience, I would love to use ETTL however my success shooting/experience in ETTL mode has been marginal. One issue is that in manual mode the markIII does not have exposure lock; If I expose on a subject and then recompose the picture, the flash does another pre flash right before I take the picture causing the exposure to be under/overexposed.

Can anyone suggest a flash strategy that has proven successful for them in outdoor night shoots, also results(pictures) would be helpful.

Thanks in advance