Regarding #3:
Here is what I'm used to... When the (last) moderator drops, the users hear something like "the moderator has left the conference" and then get kicked back to music.  If a moderator dials back in, music goes away and the users are re-joined.  It's intended to be a secure conference, and the moderator is the security, right?  Other conferencing systems I've worked with behave like this as well (not just Asterisk).  I realize we're getting into the realm of fancy features rather than a clean conference application, so I'm already prepared take a hike.  =)  Could I emulate that behavior another way?

Regarding #4:
I don't have an opinion either way on the ding sounds really - it's a cosmetic thing and I just thought I'd mention it.

Thanks!