Depending on the number of pages, your website will require between 10-20 images. This includes your logo, a nice image when visitors land on the site, images for each of your services, and a sprinkling of images for things like blog posts.
It's nice for visitors to not see the same image on every page, so if you choose a 2 or 4 page website, expect to need a few more images to keep things spicy.