To name someone or something in literature is to give it breath. To write “The woman in the white suit” is one thing. To write “Emily Johnston, the woman in the white suit” is quite another. A woman is a part of the plot. Emily is part of the story. Both may have lines, but only Emily is likely to have a history, even if it’s a brief one.
The names themselves are often important. A name is the first gift a person receives. They are intentional labels that speak of the culture and the temperament and aspirations of the family. Emily is tender. Paul is strong. Elizabeth is nobel. Names evoke the spirit of another. Nicknames are given to and usually accepted by people whose qualities are representative of their qualities – unless they are ironic, like a “Shorty” for a tall man.
For writers thought should be given before awards a name. The named person plumps a story and adds complexity. Emily has importance. A character too richly drawn may turn the reader’s eye from the main story. Too few characters can make the tale thinly drawn.
Success comes down to the writer’s craft. Hemingway did quite well with one character in “The Old Man and the Sea.” Dickens and Tolstoy used dozens with clear success. There is no right number. Just remember, writers, that a character is a guest in your work who must be provided for and attended to.