As far as I can see nothing unexpected is occurring.
You state that you want to create a new SharePoint farm using PowerShell. That implies that the server isn't part of any farm, which is what the message 'The local farm is not accessible.' also suggests.
Then running any SharePoint cmdlet (Except New-SPConfigurationDatabase) has a very high likelihood of failing as there is no SharePoint farm.
So just go ahead and run your PowerShell script to create the farm.
The advise about using Get-SPShellAdmin if you get the message 'The local farm is not accessible.' only applies if the server is part of a SharePoint farm. And then you need to run that as an account which has access to verify that the account you was using didn't have access.