1. you need proper lighting for an anemone and perfect water. Read up on thier care, if you haven't alreay done so.
2. clowns don't need an anemone if that's the reason you want it.
3. anemone needs an established tank, and someone who knows what they are doing.
IMO, I would wait at least 6 months to a year before getting an anemone.
IMO, ten gallons is too small for clowns, but other will say it's fine. My book (Marine Fishes by Scott Michael) says a min of 20-30, depending on which one, for a clown.
Make sure the tank is cycled before adding any fish.