Unfortunately I can migrate my email to FastMail, but years worth of paid Android apps will be lost if I migrate away from my Google Apps for Work account.
No need to. You can have a different email account than Google account on your Android devices.
Android allows you to have almost unlimited accounts fort unlimited things, and you can yourself control what gets synched for each individual account.
Just keep using the old Google Account for play services and the like and your new email account for fastmail email.