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.
Adding anything to /etc/hosts is not necessary, but really helps, so it will be pretty useful to add both (IPv4 and IPv6) records. After all, it is not expensive in any sense (10 seconds on each won't kill you day), but you'll know this part is done completely.