First off, welcome to the board!
Yes, you do need a filter for a fish tank. About a Chocolate Chip Sea star, I would not recommend putting them in a 10 gallon. Some people do it, but they can grow to be pretty big. I believe the average size is 5 inches in diameter, but some have been known to grow a few inches larger than that.
Maroon Clownfish need more space than that. They are also extremely territorial and the most aggressive of clownfish. The Green Clown Goby would be a great fish for a 10 gallon. At the most, you could put two small fish in a 10 gallon. Many people put two Percula Clownfish in their 10 gallons and seem to do well with that.
Hope this helps =).
-lefty