Hi there,
Yes, you'll need to to create those AV.domain.com and WebConference.domain.com (and sip.domain.com) in your public DNS space no matter what. Otherwise remote clients and federated partners will not be able to reach your edge server.
As for the Edge resolving the AV FQDN, you'll want to configure your Edge server to use your company's public DNS server. That way it'll pick up the FQDN entry just like everyone else on the Internet. You'll need to do this anyway if you want to enable Federation, since the Edge needs to be able to resolve DNS entries like (SRV) _sipfederationtls._tcp.<federateddomain> and sip.<federateddomain>.
Some companys also have DNS servers in the perimeter that resolve Internet addresses. If so, you can use that, but be sure it resolves Internet addresses in addition to perimter server addresses.
Also don't forget to set the default gateway to point to to the Internet and add a static route pointed to your internal firewall for packets destined for your corporate subnet. (The internal firewall cannot be NATed...it must have a routing relationship with the AV Edge.)
thanks,
Alan Shen
MVP and MCM