It is time for a series of questions with answers, because for some reason sometimes the hardest information to find is the answer to simple questions
How many instances can be included in a single Microsoft Dynamics 365 for Customer Engagement Online Tenant?
A tenant can include up to 50 Dynamics 365 (online) production instances and up to 75 non-production (Sandbox) instances. https://technet.microsoft.com/en-us/library/dn722373.aspx