Powershell – Free/busy information from powershell

What you're looking for is an offline defrag. The command eseutil /d will get you what you need. See the linked Microsoft KB.

Please note that when doing this, you want to put your temporary database on a different partition that has the same amount of free space that your current exchange DB has.

What you want to do is create a custom Powershell module. Start here for the official MS documentation, but there are plenty of other tutorials available online. There is also a book called Professional Windows Powershell Programming that covers development of custom cmdlets and modules. It dives deep into the .NET level. Haven't read it myself so can't make a recommendation.