I can't get my EdgeRouter setup properly

I want to leave my cable moded/router as is and add a subnet via the EdgeRouter X on port 1. Later I may add another EdgeRouterX for another Subnet. I will leave my some devices connected directly to the cable modem/router on it's ports 2,3, and/or 4. I tried to indicate the set up in a diagram. How should I configure the EdgeRouter X?

modem/router with DHCP(10.0.0.1)Port 1--|------EdgeRouterX DHCP eth0 Internet - LAN Ports (eth1,eth2,eth3 and eth4)
                                                      Port 2--|
                                                      Port 3--|
                                                      Port 3--|