As this would require two internet IP addresses and incur double the fees (US and Canada, I can't speak for the rest of the world) I wonder why this odd setup was designed.
I'd return any funds to the client as they are not going to be happy.
In parting I've done the more usual
Cable modem -> Router -> Devices and second router as a WAP
And I don't consider that difficult or as expensive as what you are trying to do.
What I'm trying to do is:
wifiA(Int signal) <-wireless-> router A <-cable-> router B (AP) <-> Devices
problem is wifiA will vary, so I need router A to have a fixed IP for itself. Router B also needs fixed IP, cause I need to get in A setup to connect to other networks. If it has dinamyc IP it's hard to know what the ip is.
biggest problem is that since I will connect to different wifi's the subnet could be 192.168.1.XXX, 192.168.0.XXX, 192.168.5.XXX
so router A would be connected to a 192.168.0.1 for example, while in the same time I need it to have an ip of 192.168.1.100 for itself. How to do that?
also I am confused on how to configure both routers in the following fields:
Operation mode: bridge or NAT DHCP client, server, off subnet mask IP of each router (does it have to be in a range? I'm using 192.168.1.100 for A and 192.168.1.100 for B)
also, how should I interconnect both routers, in 1 to 4 router A linking to Internet port router B? or both in the 1-4 ports?