The ER port 1 must be set to static and have an RFC1918 address/subnet supplied (e.g. 192.168.1.1/24). If you haven't already done so, update to 1.9, and run one of the setup wizards (IIRC, "Basic" is the one for "just simple internet / DHCP from my ISP, and eth1-4 set as the LAN"). Wizard will also set firewalls / NAT masquerade / DHCP server on the ER / other things I may be forgetting.
Not really sure what you mean by "WAN - LAN Cascade" though.