For that size tank, 3 or 4 Banded Trochus snails and a couple scarlet hermit crabs should be plenty IMO.
FWIW, I only have one Trochus snail in my 20 gallon tank an it's damn near spotless. I don't mind cleaning the glass on occasion, stirring up the sand bed etc. This combined with great water quality and you shouldn't need a CUC at all. GL.