Star fish

[Madmak]

With that size of tank almost any starfish is tricky. They need a lot of space to find the types of food and detritus they need to thrive. I'm no expert but I think you would have issues with a chocolate chip, blue, or any ornamental type but a sand sifter or brittle star might do better. The latter are more functional as well.

I do have a few in a 200G but they take some spot feeding to ensure they aren't competing for every meal.

Some more research should reveal the answers to your other questions, don't rely on the LFS too much on this subject.

Good luck with the search.