Re the v4 space question, for v4 from the public internet was covered in my original (fallback proxy switched on host header). Internally, using v4 10.x network

Re the v4 space question, for v4 from the public internet was covered in my original (fallback proxy switched on host header). Internally, using v4 10.x networks for internal systems is fraught with problems as you'll inevitably end up trying to connect other 10.x ambiguously addressed networks, and get bit by the ambiguity in security, monitoring, configuration etc. End-to-end addrssing with globally unique addresses is just a good idea, it's a big reason the internet model won over competing networking technologies.