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: 
Yes, 127.0.0.1 should be left. IPv6 is enabled, but IPv4 is still used.
You didn't mention which OS you are using.

On Windows systems, the name resolution of `localhost` is handled by the system and those entries are not needed in the `hosts` file. This is even explicitly mentioned in that very same file:

```
# localhost name resolution is handled within DNS itself.
#   127.0.0.1       localhost
#   ::1             localhost

```