User friendly slider first image=thumbnail?

Hey. I’m looking for this solution (pref. not php-advanced):

-User friendly-slider, managable inside the Add new post screen

-First image (or similar) = post thumbnail that appears
together with the post excerpt on the front page

-When inside sinlge post, slider images/attachments automatically create a responsive slider

Must be user friendly since I can’t rely on client to work with creating slides separately and copying shortcodes.
Have tried working with flexslider, calling in the attachments and not displaying the post image in single page. First of all, I can’t get it to work at all because my brain is to small, secondly, if the client only wants one image in this custom post type, they will have to create a slider with only one image (which they will forget and then complain)?

Thanks, and, doot do-di-lo doo!