If you are planning to deploy AD FS in an organization in order to federate your on-premises users to Office 365, there are a couple of things to keep in mind. The first is the number of AD FS servers that you plan to deploy on the Internal Network. This depends on the number of users in your organization. If the number of users is less than 1000, then you have to deploy one AD FS Server. In case the number of users is between 1000 and 15,ooo then you have to deploy 2 AD FS servers. And if the number of users is between 15,000 and 60,000 then you have to deploy AD FS servers anywhere between 3 and 5.
The next which one most know is the type of certificate you are going to use. In case you are planning to Install the AD FS role in a computer running Windows Server 2012 R2, then one would have to use the Service Communication Certificate also commonly known as SSL or Web Server Certificate. This certificate is used to Identify the AD FS Server on a network and also to secure communication across the network.