Multi server security on Plesk

Hi

I have this scenario and I want to see if there is something I can do to have a more secure implementation.

I have an application. I plan to put the database in a second server and also do replication for HA.

So here I thought I should have at least 3 servers (all VMs) :
1- Server 1: Application + web servers --> This server will have web access
2- Server 2: Master database server (database 1) --> This server has local access to server 1
3- Server 3: Slave database server...

Multi server security on Plesk