Efficiently loop over array, appending result to string - powershell

Question

I'm very much a Powershell beginner (if that). I've been stringing together code from everywhere to make something work, but now I want to make it a bit more manageable to edit.
I previously had this script which I had written out all, but it is very repetitive. It was a copy from source to destination, and was easy to control with 1-5 to do. I'm now up to 14, and it's a lot of repetitive code.
I'm trying to consolidate it into an easier to maintain script.
Previously, I was copying the $copy and $result lines multiple times for each share couple.
I've now moved that into an array which I want to loop over:
# shares to copy source and destination
# blank 1st entry for easier numbering
$shares = #(
#(),
#("\\nas01\share01\", "\\nas02\share01\"),
...
#("\\nas01\share99\", "\\nas02\share99\"),
)
# loop
for($parentLoop=1; $parentLoop -lt 99; $parentLoop++) {
for($childLoop=0; $childLoop -lt 2 ; $childLoop++) {
$args = '/cmd=sync /open_window /force_close "'+$shares[$parentLoop][0]+'" /to="'+$shares[$parentLoop][1]+'"'
$copy = Start-Process -FilePath "C:\Program Files\FastCopy\FastCopy.exe" -ArgumentList $args -Wait -NoNewWindow -PassThru
$result = if( $copy.ExitCode -eq -1 ) { "FAILED" } else { "SUCCESS" }
$source = [Math]::Round(("{0:N2}" -f ((Get-ChildItem $shares[$parentLoop][0] -recurse | Measure-Object -property length -sum).Sum / 1GB) / 1024 ), 2)
$destination = [Math]::Round(("{0:N2}" -f ((Get-ChildItem $shares[$parentLoop][1] -recurse | Measure-Object -property length -sum).Sum / 1GB) / 1024 ), 2)
}
$response = "$result ( Source: $source / Destination: $destination )"
}
# get the date time
$dateTime = Get-Date -Format "dd-MM-yyyy HH:mm:ss"
# compile email
$emailBody = "Completed copy\n---\n\nShare 1: $response"
$emailArgs = "-host:192.168.0.1:25 -from:email#domain.ltd `"-to:me#domain.ltd`" `"-subject:Copy report - $dateTime`" `"-body:$emailBody`""
$email = Start-Process -FilePath "C:\Program Files\cMail\CMail.exe" -ArgumentList $emailArgs -Wait -NoNewWindow -PassThru
What I don't know how to do is to add in the output of the $response for each loop into the $emailBody.
I also don't know if there is an easier way to get the share size. I thought about mounting the share (source and destination) then capturing it locally (Get-WmiObject Win32_LogicalDisk -Filter "DeviceID='A:'" | Select-Object Size) and then unmounting it for the next loop, but wasn't sure it was efficient or if I'd run into issues of "failure to dismount".
Ideally, I'd like to be able to scale the $shares array up or down, and the email output to scale too. This was I can have a plaintext email (quicker to read than attachments) that says:
Completed copy
---
Share 1: SUCCESS (Source: 256 / Destination: 256)
...
Share 99: FAILURE (Source: 25 / Destination: 985)