A general range for file size should be around 100-200 kb.
It is best to save out images as JPGs unless the background is transparent. JPGs have a smaller file size than PNGs.
Product images should be sized at 800px x 800px
To save out the images in Photoshop, it is suggested to save them out with the “Save for Web” option.
Save the file as a JPG, with the file quality either as Medium or High. The higher you go, the bigger the file size and longer they will take to load.