This plugin allows you to include photosets and gallerys from flickr in your wordpress site, either embedded in a page or post, or as a sidebar widget
The widget will take up to 10 photos, while a page or post can have up to 30 photos per shortcode. The amount of shortcodes that can be used per page or post is limitless.
Most likely yes, since it is a newer lightbox added with version 1.2 of this plugin. The Magnific Popup scripts should only be included if you are not already using another Magnific Popup plugin that adds the scripts already.
Caching removes the need to query the Flickr API everytime a page is loaded that contains a gallery or photoset, which will speed up your site. However, not caching allows you to have the photos change every time a page is loaded.