You can never have too many corys. Well...I suppose one could, but...
In a 55g, I would aim for 12 up to 20 or even 30. Don't know what other fish you have.
No less than five of a single species is a good aim, so you can have all one species like the Corydoras paleatus you mention, or you can mix species. They all get along. In my current 115g tank I have close to 40 corys representing about 10 species. Some arrived as "left overs" from the store so there may be only 2 or 3 of the species, but they all play together; I frequently see different species shoaling around together in pairs or a trio, all different, nudging each other in their antics.
Byron Hosking, BMus, MA
Vancouver, BC, Canada
Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]