However the createConnection API endpoint does not accept most of these parameters. How do I add this information to create and configure the Twilio connection using the Management API?
I agree that the documentation for individual connection options is far from ideal and I know this is being tracked by the documentation team.
Your approach of creating one through the dashboard and then obtaining its data through Management API is actually the same I use when I need to refresh my memory on the field name for a specific option.
The above does have the side-effect that getting (reading) a connection may return more information than the one you can use during creation/update, but we can compensate that by removing any root properties that cannot be modified.
For example, from a quick test you should be able to create a passwordless connection with the following payload: