A skimmer is necessary on any tank IMO. Once you see and SMELL what it pulls out of the water you'll never run a tank without one. A Coralife Super Skimmer 65 is a good option for that size tank. I had one on my first reef tank and it worked great. You can pick them up new for around $80. I have 3 fighting conchs in my tank. I'm not sure of the dangerous nature of the species available in the hobby. As for the stars they're pretty safe. They are sensitive to water quality so they should be added once the tank has matured
A side note, I would consider running a sump. It makes life MUCH easier and the tank will look much better.
A side note, I would consider running a sump. It makes life MUCH easier and the tank will look much better.