You can automate like this (based on http://www.djcbsoftware.nl/code/mu/mu4e/Compose-hooks.html).
;; Always BCC myself
(defun my-add-header ()
"Add CC: and Bcc: to myself header."
(concat "CC: " "\n&...
I came up with this pure mu4e solution. M-x my-mu4e-header-mark-duplicated will mark the first of each duplication message set (defined by identical :message-id and :flags) in *mu4e-headers* for further actions. Set (setq mu4e-headers-skip-duplicates nil) as this requires duplicated messages to be visible in the *mu4e-headers* buffer.
Have you tried C-c M-n while writing the message? This at least should cover part of the answer.
Regarding the visibility of the return receipt pop-up in mu4e, according to this thread such functionality does not exist at the moment