I am using an ER605 without a controller.  My network setup is as follows:

WAN: Zyxel FWA710.  Setup with Dynamic IP.  FWA is setup in IP Passthrough Mode.

WAN1: Sky SR203 FTTC.  Also setup with Dynamic IP.  Note that when this goes down, you get an error page if you try to use the connection.

LAN2: Solaredge

LAN3 Netgear R7000 in AP mode

LAN4: Desktop computer

The area that we live has periodic issues with both the FTTC and the FWA.  The FWA issues tend to be slowness during high usage times.  The FTTC has problems during storms.  They both have similar bandwidth normally.

I have two primary goals for the ER605, in priority order:

1. Ensure that all devices still have internet if either WAN goes down.
2. If both WANs are online, balance the load effectively to maximize throughput.

I've tried a variety of configuration settings on the ER605 (load balancing, bandwidth based balancing, failover, etc).  However, I'm having a hard time achieving both goals.  I was able to use rule based routing to give one WAN to the desktop and the other WAN to everything else.  However, if either WAN fails, devices loose internet. 

Does anyone know the right way to set all these different settings to make this happen?

Secondarily, the SolarEdge has trouble maintaining a connection through this arrangement.  Not sure if anyone has specific experience using that and if there's something specific I have to setup for it.

Thanks in advance!