Thanks for your quick response Josh.
This method seems like a conflict. My understanding is tha tupgrading ESXi involves upgrading the file system too. If I install a new VM on the old FS and then use it to backup the host and itself (the VM with vCenter) I have to wonder if it's even possible. If it is possible, then it still seems a risk since I cannot restore anything without the VM.
My understanding is that vCenter requires a Windows server. Is that not correct?