I just call up RefTeX by hitting ctrl-x + (or "C-x +" in emacs parlance). This calls up a list of all possible references and a fuzzy search box which lets me narrow it down. When I've found my reference I have ten options, including:
f1: Open associated pdf, url or doi
f3: Insert the citation into my thesis and then be asked for what kind of note I want to add (footnote? Title? author name? Year? Just a bibliography entry?), then any text to add before the reference (eg, "This argument has been made by,"), then after (p. 67). -- This answeres your question
f7: Attach pdf to email
f9: Show notes, if there's an .org file of the same name.
f10: Add pdf to library
If RefTeX can't find my query, not only does it ask if I want to add a new one, it asks whether to search various databases for it including arXiv, DBLP (computer science bibliography), Google Scholar, Bodleian Library, HAL, Library of Congress, British Library and others.
Adding entries to the database is as simple as editing a plain text file, and BibTeX provides quick shortcuts for all the different kinds of entries, checks them for you and provides a sane and customizable key.
Everything is completely integrated - my writing, my pdf library, my org notes, my bibliography database, my email as well as my thesaurus (wordnut), my pdf reader (pdf-tools) and my git repo (magit). It's just brilliant. All together it makes emacs the ultimate writers tool, as far as I'm concerned.