If you were to get one of the dwarf species, get 6.
I would refer you to seriously fish to look them up as the database on here only has one of them (habrosus, under salt & pepper cory) but there seems to a problem with the site at the moment. Word of caution about cory common names. There is the dwarf salt & pepper cory and the larger peppered cory, don't get them confused!
I would also recommend keeping cories on sand, or perhaps very smooth gravel. Cories like to grub around on the bottom looking for bits of food. Sharp gravel can cut their mouths, and gravel is harder to keep spotless than sand so these cuts get infected more easily on gravel.