Well my caulerpa eating monster is a Eibli Pygmy Angel fish! Tang will probably like it too, but your tank is on the small side for tang I would guess. I think they need 100 gals + as a minimum or so I have read, as they like to "keep on swimming, keep on swimming"!
C. Prolifera is very fast growing and I think it looks very nice in the sump, but I like planted f/w tanks too. Nitrates will drop quickly once the substrate begins to be colonised and the caulerpa kicks in. Just make sure you remove some every week.
Xenia grows fast in my tank and makes a good nutrient exporter too. I am due to take a bag to the LFS soon.