You don't need snails, crabs and shrimp. You don't have to keep any of those creatures for any other reason besides you like to look at them. You will clean the glass yourself with a mag float and/or scraper, correct?
that, and power heads positioned optimally to limit uneaten fish food and poop from settling and you are good to go.
remember, whatever you put in the tank must have food to sustain it.