There is no way within the product today for drives to be named simply buy their drive letter and not include the label without editing the volume name and removing the volume label manually as you're already are doing.
Volume thresholds for linear gauges on the Orion web console can be changed globally by going to "Settings -> Orion Thresholds" as pictured below.
Creating alerts for specific volumes is farily straightforward. Below is an example for alerting on a single volume when it exceeds less than 5% of available space.
Here's another example that shows how to do this same type of alert for multiple volumes. More can be added to this trigger condition as needed.
You can also do this node based as well as the example below demonstrates.
