How do I prepend the Abstract to the memoir MMD which will precede Contents and not be numbered?
All you need to do is place a level-two document at the top of the outline, called ‘Abstract’, and it should handle it appropriately. So with a base header level of 1:
Draft/
Folder/
Abstract
Chapter 1
Section a
...
Articles will probably be using a base header level of 2, so in that case you wouldn’t need a part 1 folder, and would go straight to Abstract at the top.
This still seems to place the Contents table first… I need to have an Abstract page following the title page immediately, then the table of contents, then the rest.
Hmm, okay, I thought Memoir’s abstract allowed for that. You might need to fiddle with an XSLT to pull that off, then, or fix the LaTeX file after you compile each time. I’d check out Memoir’s documentation and see if there are any options for placement of the abstract environment, and if not, just manually move the table of contents down in the XSLT.
Turned out to be a bit tricky – memoir.xslt hard-wired table of contents before \mainmatter, and abstract support was in the latter. I ended up emitting \tableofcontents et al. right after \end{abstract}, together with lists of figures and tables; also interspersed \clearpage after each. My fork of Fletcher’s MMD with those changes, called memoir-thesis.xslt and memoir-thesis-xelatex.xslt, is at
github.com/alexy/MultiMarkdown
In the process, I opened, for the first time, memman.pdf, the manual for the memoir style. If you’ve not seen it, you’ve seen nothing yet! Hacking multi-layered MMD immediately looked plain and simple. 
I have indeed read large portions of it. And yes, that class can do a lot.