Maybe someone can correct me if I'm wrong but only nodes that join an existing cluster have to be "empty". By the time you create the cluster the first node may have VMs running.
This is about 99% sure, so you probably want to have a backup that you can restore, just in case.
The thing is that you won't be able to change the IP address after cluster creation. If you're already absolutely sure about your hostnames and addresses, you can of course also create the cluster right now.