I have run a NPS for several years with sun corals, NPS gorgs, anemones, and feather dusters. Problem number one is feeding. Every critter had different food size requirements. For example, a blueberry gorg needed a different size food than a Dendro. On top of that, they had to be fed several times a day. If you go away for a few days, you may come home to death. It has happened to me. Another thing is lighting. Bright light indirectly will kill NPS. Algae forms on the animal and smothers it.
Not so much with sun corals but with gorgs and sponges.