I agree with Tre any nano is way way too small for an anemone. Besides, the water parameter fluctuations that are bound to happen in a tank that small would undoubtedly do in a nem in no time at all. They require pristine water conditions and and established tank with really good light.
Clowns are too small for a 5g also, in fact I wouldn't put one in a 10g. The only thing I would think about in a 5 would be as Fool said....neon gobie, clown gobie or a yashi gobie & shrimp pair....