I need to know the height and width for both the full-size image, and the thumbnail. I saw somewhere that the width of the full-size is 900 pixels, but I don't know what height to make it. What about the thumbnail? I'm assuming the images are to be 72 dpi. Also, does it matter whether I save as .jpg or .png? Thanks

-The size should be the same or bigger than the FPSS module dimensions (height and width).
-It doesn't matter... FPSS turns all the formats (unless you uncheck the option) to jpg.