Welcome to the Community - really sizing the VMFS datastore is going to depend on the size requirements and the loads that will be placed on storage - fro best practices info you can check here - http://pubs.vmware.com/vsphere-55/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-55-storage-guide.pdf
I have also moved this to a more approrpiate forum