hi again, I understand that you need to deploy a virtualized environment using as base operating system Ubuntu 18.04+ KVM. In the base system (sda Disk 1) you will need to install Nginx, Apache2 and an SMTP server. Then you need to create two virtual machines, one of then with ubuntu 18.04+MySQL(Disk 2) and the other VM ubuntu 18.04+Libreoffice (Disk3).
Do You need the Disk 4 as Spare for the base system? It can be achieved in the installation time of the base system, so we can set up a RAID 1 scenario. If disk 1 fails, the disk 4 take the control.
For Internal network communication, we can use the linux's bridge feature, in that way we can insolate the Database's and template maker's network.
I don't understand what about Template maker, can you provide more details, please.
You can ask without commitment!
Regards!