What are the best ways for creating galleries from images stored as entities?
Hey you can use the Galleria module in D7. Here is a quote about it (from the module's project page):

... allows users to create image galleries using the Galleria jQuery plugin, found on http://galleria.aino.se.
There are several different approaches of using this module to create Galleria image galleries. The most typical and easiest way to do so is to use it as a field formatter for image or media fields. All images uploaded to such a configured field will then be displayed in a Galleria gallery.
You can also use it in conjunction with the References module to build a gallery of image nodes, referenced by a 'Node reference' field; or you can use the Views module to gather a list of images to display in a Galleria.