Hi Matthew,
This is an issue that has been extremely frustrating for me. Here is the solution:
To disable the "Let's finish setting up your device" prompts on Windows, navigate to Settings > System > Notifications & actions, click "Additional settings," then uncheck the "Suggest ways I can finish setting up my device to get the most out of Windows" box.
Hope this helps. This setting should be disabled BY DEFAULT. It is a shame that companies like Microsoft have determined that repeated cash grabs like these which harm user experience are more important than the actual user experience and long term customer satisfaction.
Best regards,
Chris Dyson