Adding one node in the cluster is pretty straight forward. You can check the link below:
You can first create 5 machine using cloning which save the time of configuring.
You need to check the IP or if you are using centralised server then you can use the hostname as well if not then you need to configure the IP of the System and add the same to the Namenode(slave configuration).
After configuring, you need to either use
start-dfs.sh in Namenode
hadoop-daemon.sh start datanode
Hope this helps.