A portfolio item can link to a page, post, URL or open a lightbox. You can have image and video items. Any post type can be the source of your portfolio items. An easy method to keep your items organized is to make them all sub-pages of a main “Portfolio” page then select the parent page as the source of the items. It will automatically generate items like those shown below from the child pages.
My Portfolio WordPress Gallery
Below are portfolio samples. These items can be arranged in any number of columns, items per page, paged, image size and much more.