Question: I am new to unmanaged VPS servers and in addition IPv6. Is it necessary to include 127.0.0.1 AND ::1 for localhost in /etc/hosts files for IPv6 enabled servers, or is ::1 alone enough?

Answer: 
Leave the hosts file alone. Fiddle with it and you may break something. For example, if you remove the `127.0.0.1` don't be too surprised if anything that uses `localhost` fails.
On my mac, I could not access localhost. When I commented out the line "::1 localhost", I was able to access localhost again.