The size tank and livestock have a lot to do with what starfish you can get. So, I would also like to know the answers to Meowzers questions.
I also recommend getting a variety of snails rather than a starfish. While starfish are cool to watch, most starfish are unsuited for home aquaria. Eventually, they will starve to death. Most starfish are filter feeders, coral eaters or detrivores. Detrivores mean that they eat the microbes, waste and microfauna that is in the sandbed. Besides asterina starfish, I have never known a starfish to eat algae.
If you have an algae problem, I suggest reading about how to get rid of that particular algae. Each algae has a different way of how to get rid of it. I suggest that you take this approach.