Power Store has a gallery built in.
In the Power Store admin go to Content -> Galleries to create a new gallery.
once the gallery is created, go to Content Manage section. Select Home Page - Site Message content area to edit the site message. On the bottom row of the HTMML Editor toolbars, the last button to the right is the add gallery button that will allow you to add the gallery to your site message.
You could probably use a third party gallery as well, but we cannot offer support for that, and it would probably take some hand coding.