If you allow 8MB-12MB uploads (which I recommend, since it's about the highest I've seen from cellphones), you'll end up with images around 400k-700k (depending on compression and full size dimension). They'll be resized to the full size dimensions only if the image exceeds that dimension (I allow 1920 as the max).
The FILESIZE is determined based on the image dimensions and the compression; it'll vary by image, especially using an image with a lot of detail.
When you click on an image and it opens in the lightbox, or you display inline, it should display the image with the css "max-width: 100%;"; which means as wide as the screen allows before trying to stretch the page.
