Purchased this on Craigslist... Help a newbie out... (90 gallon saltwater)

Welcome, if I was buying lights I would be tempted to hit Craigslist again, and look for some led lights, or take the plunge and look at some of the cheaper units from some of the sponsors here, I bought the proton32s they are very nice, I believe there is a 48 inch version.
I dont have any sand in my sump, just a load of broken live rocks (I get a good deal from one of my LFS for the rubble in the bottom of their tanks/boxes)
This hobby can be as cheap as u like or as expensive as it needs, the driver here is you and what you want to see, I understand the fowlr approach, that will set you up to one day move into corals, providing u always buy everything with the view of one day popping a coral or 2 in there, the lights are the main change, do it now, and save money on bulbs and replacements later.

 

if i am right, that is just a RO unit and not a RODI unit; you should get an RODI unit instead