to design a network

I need to design a network with 5000 nodes, that has four main locations that are primarily Ethernet.There is a legacy 100 nodes of Token Ring attached to a mainframe. Cisco or Foundry routers connect the Four main locations, with switches employed. Other connections to these sites are done via DSL or ISDN. I’d like to find out how many routers,switches and so on I need for that kind of network. Thanks