What is the purpose of having 4 routers, where 1 would be sufficient?
In regards to access to servers: consider dividing into 6 VLAN’s, 3 server VLAN’s (per network) and 3 client VLAN’s per network.
Access can then be easily handled by the correct firewall rules.
Love to link this topic: http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1