photoshop tells you the size of the photo in mb or kb vs. the image quality (i usually go with 60 quality) when you choose "save for web".
photos don't need to be much bigger than 600x600 pixels (found under image size) to be viewed on my screen.
a jpeg made like this is generally around 600k, which i think is short for kb.
ebay has links to sites which will host your photos for display on the internet.
hope this helps.