Red blood cells are primarily for carrying oxygen and carbon dioxide through the use of hemoglobin. A red blood cell life span is about 120 days. White blood cells are cells of the immune system that are involved in defending the body against both foreign materials and infectious diseases. The average life of a white blood cell in the human body is only 3-4 days.
Image of red and while blood cells under a microscope using a blue stain.
At 400x magnification the nuclei of a blood cell is visible. At 1000x magnification you will not necessarily be able to view particles you could not see at 400x, the cells will simply fill up more of your microscope field of view.