even percula clownfish are probably a bit big for a 5.5...you would be better sticking with the goby; but, yes, you could keep a sexy shrimp with a clownfish
ok, im still gonna wait a long time bfore putting anything in the tank, ive seenfalse perces in 6 gallon nano cube that are just as big if not small. im just gonna add corals once the tank is ready then see what what fish there are.
most shrimp, like the red banded shrimp do best with one. they will kill each other off. and a clown should be fine in a 5.5g. i know people who keep even an ananome, but yes i know that pushes it.