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Not sure what you mean by IPv4 fallback IP, but all IPv6 Proxies may be used only via IPv4 Address in CP. Number of IPv6 Proxies that you want to generate may be set-up when installing in template or even cloud tools. Number of IPv6 proxies depend on hardware and or subnet.
If you want use No Blacklisted IP's you may try IPv6 Proxy generator template in Merchant Tools, Basically you may need just provider that is giving IPv6 subnet and CENTOS 7. Please note, that Im not providing any free support for templates installation as some providers may need own template to work properly.