If I understand what you are saying, when you connect the port on the OpenWrt router that you have configured as a WAN port, you do not get an IP address on your computer. This is the correct and expected behavior. Note which port this is -- and connect your ISP modem to this port.
Connect your computer to another port on the router (the others should be your LAN. Your computer should get a DHCP issued address from the OpenWrt router -- verify the address you get and post it here (it should be something in the 192.168.1.0/24 network).
In LuCI, the main status page should have a section for "IPv4 upstream" -- you should hopefully see a valid IPv4 address from the ISP in that section. Please verify that (bonus -- you can give us the first two octets which will help us validate that it is working as expected while not revealing your complete address).