Looks like you have nearly everything you need to me. You will need another body, the 5DII would be awesome if you can get some time with it beforehand so you are familiar, if not get another 7D.
You will need 2 more flashes and one more light stand so you can have 2 remote and one on each camera.
I think you can do the shoot with with your Sigma 17-50 2.8 OS and the Sigma 50-150 2.8 OS on two bodies and not have to worry about switching lenses.
I would suggest having a total of 6 16Gb cards if possible.
If I lived nearby I would be glad to help you out just for the fun of it
