Serpent starfish would be happy and fine in there. They're not pretty and hide alot through, but they're cool and benefical cleaning up after other livestock. They're actually the most harmless starfish despite how much of an octopus they seem.
If your tank is a year or two (preferably 2) then red fromia can be atempted.. most starfish other than those are not reef safe.. These are also harmless as they are very diet specific.. biofilm which is only present in large, and old established systems.