Hi David,
We have a wiki for JA Voice (http://wiki.joomlart.com/) but a pity it is currently down at the moment (it will be back online on coming Monday).
For the time being, I would like to answer your questions as follows
<blockquote>
1. Can JAVoice be used within Jomsocial or other social networking groups (so that other groups cannot see the entries)?
2. Can JAVoice’s moderation of group entries be assigned (and restricted) to members of the same group?
</blockquote>
JA Voices & JomSocial use core joomla usergroup as the user hub, however groups in Jomsocial is not supported. For both 2 mentioned fearures, it will require a few custom coding which you can post on joomlancers.com. I believe with a budget of <$300, you can get this working