How many licenses do I need to purchase of Server and Client versions

We are a school with 6 servers and 400 Windows 10 workstations. We currently have Sophos Endpoint installed on our network.

I am interested in increasing the security particularly in light of recent ransomware incidents and have been considering Intercept X

My question is that given all student and  teacher files are redirected to the servers, (the workstations don't hold any user files) would we need to implement Intercept X on all servers and all workstations or would it be effective just deployed to the servers where all the files and data are stored.

Regards,

Neville.