Replacing Gateway Servers in a Clustered Instance

Hello;

We need to replace all of the servers in a Power BI Gateway Cluster (upgrading from Windows Server 2012 R2 to 2016).  We have three servers in the cluster today, and our plan to do the upgrade is as follows:

1.  Build a new Gateway server (Server 2016) and add it to the Cluster (server is 04).  

2.  Remove server 03 from the Cluster, rebuild it with the same name but running Server 2016, and add it back to the cluster.  Continue this process with servers 01 and 02. 

My questions are:

1.  How do you remove a Gateway from Cluster?

2.  The Cluster takes on the name of the first gateway, so what happens when you remove that server from the cluster?

3.  Are there any issues running a Cluster with different Server OSes, as long as the version of the Gateway software is the same?

Thanks in advance!