Is this RODI setup correct?

[Buckeye Field Supply]

Yeow. Someone sold you a less than ideal set of prefiltes. Assuming you are on city water w/o chloramies, a good combo is a 1 micron sediment filter and a 0.5 micron carbon block. GAC prefilters really have no place in the high capacity systems we use in this hobby. Really no need for a third prefilter, but you could use a second sediment filter or a second carbon block if you'd like.