cories won't "clean up," they will just eat the food that gets to the bottom quickly. getting cories means you will have to get food specially for them, such as sinking pellets. they can't just eat what the other fish haven't because they wouldn't get enough.
saying that, any fish will eat food off the bottom so "cleaner fish" aren't really needed.
however, if you do want cories, they don't need as much surface area as other more predatory catfish due to their sociable nature. i've seen shoals with cories piled on each other lol not because the tank was too small, because they just like being close to each other!
anyway, think about it.
what size tank do you have?
if you do decide to go with cory sterbai (beautiful fish btw) then i'd get about 6 of them because you get much better fish when theres more swimming around together. also, keep in mind that they prefer higher temperatures.
pink.