It is advised that all organizations do a proof of concept to adopt any new technology. It is the same with Office 365. When you are evaluating a new technology that you are not familiar with, it is always recommended to pilot this new technology in your organization to improve the chances of a successful project.

To plan according to the size of your organization, you will need to perform a set of tasks related to the base service and to each specific workload, such as planning according to your environment.