If we are NOT overclocking the S3 then we can just plug in 2 PSU PCI-e Connections and leave 2 empty?

??
1 connection to each board in S3 is ok if not OC, is this correct?

?
Thanks
That's correct. You'll probably never need to use the other two.
When first announced the hash rate was suppose to be 504 GH and the extra pcie's were for overclocking above that.