@1: OpenVPN TLS-over-UDP is openvpn-proprietary and is not documented in an RFC, for all I know.
@2: check the openvpn.net pages , e.g.
http://openvpn.net/index.php/open-source/documentation/security-overview.html
for details of the openvpn protocol
@3: the openvpn 2.3 release (which is scheduled for july) should support IPv6 both inside and outside the tunnel