View/Find all compressed files on the server?

The compressed indicator is stored in the "attributes" property. This Powershell will report compressed files.

gci -r C:\search\path | where {$_.attributes -match "compressed"} | foreach { $_.fullname }

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The file size is stored in the length property, which is in bytes. You can use whats called a "calculated property" to display the size in kb,mb,gb, etc.

$col1 = @{label="Size";Expression={$_.length/1mb};FormatString="0.0";alignment="right"}
$col2 = @{label="Fullname";Expression={$_.fullname};alignment="left"}
gci -r | where {$_.attributes -match "compressed"} | ft $col1,$col2 -autosize

If you want only larger files, say greater than 1MB

gci -r | where {$_.attributes -match "compressed" -AND $_.length -gt 1mb} | ft $col1,$col2 -autosize

Folder size is also possible, a slightly different beast. Just try google'ing "powershell folder size" lots of posts on how to do that. There are also many free tools (windirstat) to report folder sizes.