The PowerShell script to create a new room mailbox has been updated to Version 1.1.
The new release supports adding of a phone number to the room details. Issue #2 is now closed.
Creating a separate security group for calendar booking is still open as issue #1.
You can read the original and up-to-date blog post here: Create a new room mailbox with security groups
The PowerShell script to set Client Access mailbox settings based on AD group membership has been updated.
The issue fixed had been registered as issue #1.
The new release version is v1.1.