So I wanted to port forward the router itself (192.168.7.1) to WAN so I can view my cameras on my main network.
Here is a diagram.
I am not sure what to use for port forwarding port 8080 to my main router so I can view it on my Surveillance System.
Do I use the LAN network on the Source or on the Destination and do I use the WAN network on the Source or on the Destination.
I don't think this is what you want, unless the service that you will be using actually resides on the router. In other words, if you are connecting to a camera or an NVR, you want to forward a port directly to that device since the service is running on those devices, not on the router itself.
What is the purpose of the OpenWrt router in your network? I ask because it may not really be necessary to use as a router (for example, if you're just using it as a wifi AP, you can configure it in a "dumb AP" mode instead of operating as a router).
How do you normally view the cameras? Do you have an NVR? or just one or more cameras not connected to a central NVR? This will impact the destination.
Finally, does your main router provide you the ability to add static routes?