Sharepoint Environments

Hello.  I'm new to this community, however I work at a Financial Institution as the Product Manager for O365.  Our company is in process of building our vision/strategy/roadmap across all of Office 365.  We are in the middle of internal discussions around how many environments are ideal to support O365.  Specifically, the question around Sharepoint came up and how other companies are developing custom sites, migrating them for testing and ultimately, production.  Does anyone have any information to share about how this works at your company?  Thanks in advance.