That sounds like a fine idea. I did something similair with my frag tank, though mine has no frags yet. I divided off half and used it for skimming and pumps. I have a hob fuge on mine though and you could make two chambers, or just have chaeto free floating. I think that 4 T5s would help much more for growth and type of frags you could grow. You could try a custom flow system on your frag tank like mine, and depending where you get you pump, and what kind you have all the flow you need for 20-40$. If you intend to keep sps Id find an average in sump skimmer, and that would help with having fish also. I like your idea of having bangiis in the other side, as sort of a nursury breeding side. Maybe they could live off the pods and various others in the frag that? Sounds great so far. I have some filters, skimmers, and sand if your looking for any in the future too. Picture will come later as I just found that one of my siblings ran off with it.