Sometimes some of the standoffs come already installed; check that out.
6 would work if you really really are anxious to get started.
Put them in the corners, and the middle of the sides to give you some support.
I would contact Corsair, and they will send you some more.
In the mean time, why not test your new rig outside of the case?
It is a good way to check things out. If your mobo does not have a power switch to get you started, just touch the twp PWR leads with a screwdriver.