Whatever you add to the tank will have to have food to sustain it, or it will slowly starve to death. A cleanup crew is not necessary at all, and you can have a perfectly healthy tank without any snails, shrimp, crabs, or starfish. I would not look to online vendors for advice, because what they do is sell livestock. Like Dav3 said, get a few things because you like to look at them and want diversity in your tank, but not because you feel you need them. The cleaner wrasse despite the name is not a creature that helps eat uneaten food and fish poop, it eats parasites off of fish in the wild, and in many cases, will not eat prepared food in closed systems. As also stated, not good for your application.
the tank so far
. You don't have to limit your self to just a cleaner shrimp invert wise though, you could also add other shrimp (I'd avoid a pistol with a cleaner in this small tank but any others are fine) or a pom pom or porcelain crab are both cool crabs that tend to behave nicely (some crabs have a tendency to go rouge)
