|A few thoughts on the image as per your request.
The focus, you know about; though it has more to do with the 2.8 f/stop than where you put the focal point. Since the subject is lit by flash I can see no reason you went so narrow with the focal plane.
The toughest part for me was the crop. Since the subject was the powder on her hands and the cloud it made, pushing that main subject out to the edge of the frame seemed to lessen the impact. Too much of the image is her backside, which would have been fine if you had squared off the crop, but in this tight squeeze seems to pull the eye off the powder.
But you asked about the lighting. For the most part it works, especially for a first effort. The rim lighting especially across the small of her back is too hot, it could have been half as powerful and still have given you the definition you wanted and not have blown out the textures, and pulled the eye off her hands as much. It does work very well across her hands, so perhaps you just wanted to use a GOBO to flag it down a bit on her back.
The light on her hands and front seems a bit too tight, with an odd pattern of fall off and a strong shadow under her arm. The light works very well on her chin and throat, but so bright on her hands that the tape doesn't have enough contrast against her skin. Had you pulled the light back and dialed it up a bit you might have smoothed out the fall off and evened up the effect.
Given all the different pools of light, the eye tends to linger on the model instead of seeing her as the source of the powder. On the whole good job, I hope I have helped a bit. If you really want to get your flashes working for you, you could do worse than spending some time reading over at Strobist