If you want coral, you'll need to lose the choclolate chip star. In fact, I don't trust them or any of the knobby stars, as they're opportunistic carnivores that will have no trouble taking down a sleeping fish.
Your urchin might be a problem too, depending upon which one you have.
As for the damsel, if you want to keep other fish, I'd try to get rid of it, as it will likely pick on any newcomers to the tank.
Filtration-wise, if your HOB filter is oversized, it MIGHT work for you (It should be at least rated for twice the volume of your aquarium), but I'd go with a sump-based system, esp. if you're planning on keeping coral.