The main thing you are missing is function copy-region-as-kill
.
(defun copy-and-comment-region (beg end &optional arg)
"Duplicate the region and comment-out the copied text.
See `comment-region' for behavior of a prefix arg."
(interactive "r\nP")
(copy-region-as-kill beg end)
(goto-char end)
(yank)
(comment-region beg end arg))