Just weighing in on the starfish question real quick. Both serpent and brittle stars are coral safe, but the ubiquitous Green Brittle Star has been known, on occasion, to attack, kill, and eat fish, so I'd avoid that particular one.
Beyond that, size is the biggest limiting factor. Fromia starfish are reef safe and very beautiful, but need far more surface area for grazing than a 29 realistically can provide. I kept one in a 55 for about 6 months before it crawled into a stinging mess of tentacles and got itself killed. LOL
Someone stop me! Please! But... not just yet...
55 Gal Tropical FW
55 Gal Mixed Reef