-I assume that by parenthetical citation, you mean the Harvard referencing system. Yes, in that case you write the last name of the author followed by a comma and then the year in which that article appeared (in case of an article being cited). For example, if the article you need to cite is by John Doe published in 1405, then you would write (Doe, 1405).
-For including external sources, use endnotes like you mentioned. Add a superscripted number next to the idea, and then include a Notes page.
-If you are planning to include a Sources Cited page as well, try considering an alternative. Include a References page that includes all the sources in one go. That way you do not have to include the Notes page. What I mean is, use a citation style throughout your essay (for example, consider writing numbers in square bracket ,  etc.). After that in the References page, give the complete description of the citation. As an example:
 Doe John, A treatise about blah and blah, Journal of Blah (1405).
-If you are insistent about including a Sources Cited page and wish to work using Endnotes, then you can do the following: in the Notes page elaborate on all the endnotes. After that have two sections in the Sources Cited page, one section having internal citations (i.e. citations from class reading) and the other as external citations (which should essentially be the same as Notes page). This would lead to a repetition though.
-To avoid above repetition, consider changing the Sources Cited page to Class Readings Cited or something similar. In that way, you can have the Notes page in place and also have a page for internal citations. This, in my opinion, should solve the dilemma.
-You can either have a Sources Cited page or a References page. Some of the other method of elaboration of inline citations need to be present. Yes, you need to put class readings in there too. That's what your teacher has asked you to do.
-For starting ideas, I would recommend launching a full attack on the subject by jumping right into it. Do not look for fillers etc. Like John has mentioned above, go directly to the matter.
-You can include a word count as a small footer towards the right side of the end of the main text (before the Sources Cited or References page), though this is not a mandate.
Hope this helps!