4 PCIe Slots right, but u see that u have not enaugh space for the card in the second PCIe slot for the cooling.
so if i would build such a system, i would only put 3 vegas in.
or change the motherboard into the asrock taichi or the msi gaming pro, which have anaugh space for the cooling of each card.
And the Fans... you will need much of it, but you will need realy fast ones to get the heat in the case under control.
And then this will be really loud

what case u want to use?