The answer? As many as you need to to answer all the questions in your mind (or anyone else's) about the story. In my case, a whole heap. Here are just some of the sources I turned to when researching the world of The River Nymph. I haven't included all the Internet sources or the books I checked out of the library. I love doing research. But sometimes you just have to stop and start writing!
Like a Family: The Making of a Southern Cotton Mill World
Jacqueln Dowd Hall, James Leloudis, Robert Kortad, Mary Murphy, Lu Ann Jones, amd Christopher B. Daly. W.W. Norton & Company, 1987
Hard Times Cotton Mill Girls: Personal Stories of Womanhood and Poverty in the South by Victoria Byerly ILR Press, Cornell University, 1986
Let Us Now Praise Famous Men, by James Agee and Walker Evans, Houghton Mifflin, new edition, 1988
You Have Seen Their Faces: Margaret Bourke-White and Walker Evans, University of Georgia Press, 1995
A History of Stroke: Its recognition and Treatment, William S. Fields and Noreen A Lemax, Oxford University Press, 1989
Ordered to Care: the Dilemma of American Nursing, 1850-1945, Susan M. Reverby, Cambridge University Press, 1989
Central Georgia Textile Mills, Billie Coleman, Arcadia Press, 2017
The Sears, Roebuck Catalogue, 1927 Edition, Alan Mirkin, editor, Crown Publishing, 1970 (edited reproduction of the original catalog)
Honey Lou, or the Love Wrecker, Beatrice Burton, Grosset & Dunlap, 1927
The Flapper Wife, Beatrice Burton, Grosset & Dunlap, 1926
Dorothy: The memoirs of a Nurse 1889-1989 Dorothy Moriarty, Corgi Books, 1991
Notes on Nursing: what it is and what it is not, Florence Nightingale, Dover Publications, 1969
District Nurse, Faith Baldwin, Triangle Books, 1932
Arrowsmith, Sinclair Lewis, Signet Classic, 1961
The Reader's Companion to Cuba, Alan Ryan, editor, Harcort, Brace and Company, 1997
Havana: Portrait of a City, Juliet Barclay, Cassell, 1993
Cotton Mill Girl: A Novel, Flora Ann Scearce, Tate Publishing, 2006
Call Home the Heart, Fielding Burke, The Feminist Press, 1983
Anais Nin: Journal of a Wife, The Early Diary of Anais Nin, 1923-1927, Quartet Books Limited, 1986