I don't think the second curtain sync would have a useful effect unless you have a moving background vehicle that you want lit up at the end of the tail-light trail. There is some concern that second curtain sync will sometimes contribute to droopy eyes, as the preflash that the camera uses to estimate exposure causes a late blink that is captured by flash at the end of exposure. Google BEETTL syndrome and you will come out with complaints of Blinking Eye E-TTL on the Canon system. Anecdotes on the 'net say that it is less marked if the flash fires at the beginning of the exposure, because the subject hasn't had time to blink with the preflash.
As to the balance of exposure, back to front, I think that would be a trial and error thing that you could adjust at the time, based on the histogram and instant review. To me this is the equalizer, the greatest advantage of digital photography.
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