Do you think that I should start dosing Iron in the tank?
I would test first. Check out what this says about dosing iron, among other things- http://www.reefkeeping.com/issues/2004-05/rhf/index.php
Do you think that putting the skimmer chamber in the new sump after the refuge would be a good idea?
I would put it before the fuge. IMO
that would be better b/c then you have less DOC
's getting into the rock, LS
, and/or mud in the fuge. Your skimmer will perform best when getting surface water directly from the tank, before anything else filters it. I run my sump w/ the skimmer before the fuge, and many pictures I've seen of sumps are set up the same way. I've never heard of it being an issue. HTH