Unfortunately it seems Yerevan, unlike other US Consulates, does not post official supplemental DV information - this would have been rather useful in fact:
http://travel.state.gov/content/dam/visas/pk 3 supplements/YRV - Yerevan.pdf
They might be posting information directly on local US Consulate websites, though, you'll need to do some research. Again, the objective is to get a good understanding of local DV processes and peculiarities, if any - there certainly is no harm to ask for local US Consulate advice and direction beyond general DoS information available here (I would wait until you have the exact appointment date with the Consulate):
http://travel.state.gov/content/vis...re-selected/prepare-supporting-documents.html#
As mentioned, it might also be useful to get some reliable first hand interview experiences from DV folks in Armenia, subsequent to their interview, this turned out to be rather useful in our case.
Last but not least: Passport & Visa Return after Interview (excl. additional AP etc.), anywhere from 2 to 14 days, the latter happened to be the case for us, for example.