Are there a large number of cholesterol molecules in the plasma membrane of a single human red blood cell or merely a few?

Large number. Cholesterol molecules are found in every cell of the body, and are especially abundant in cell plasma membranes. The plasma membrane is a continuous double-layer of phospholipids, interwoven with cholesterol molecules and proteins. So, cholesterol molecules are found in great numbers in the plasma membranes of red blood cells.