I don't like it. The focal point is going to be that big honkin' tank, I think putting a little frag tank next to it would be barely one step up than having a frag rack on the side of the glass. Plus you got 3 feet of width to that guy, that 3 foot side is a viewing pane, you really want to block it? Why bother with starphire then then? Now if one of the sides is going to be "hidden" (in a fishroom or something) then year sure go for it.
If this was me, and I was intent on plumbing together a frag tank, I would either put one under the tank in the stand, or integrate a piece of the sump as a frag tank. Not sure how much space you want to keep free under your tank for equipment, or how big your sump will be.