Hello Sean,
You can use Get-NaDisk to get started with your script.
Here's an example below where i use the where-object to filter out disks which belong to a raidgroup and also use measure-object to count the number of disks in the raid group.
Get-NaDisk | select raidgroup,aggregate,name,shelf,bay,status,physicalspace,RPM,FW,model,pool | ?{$_.raidgroup -match "rg0"} | select name | Measure-Object
