I'd like to purchase an ER703WP-4G-Outdoor gateway but want to ensure it will be compatible with my use case.

I have an ER8411 router with my main ISP hooked up. I also have a SG3452 POE 48 port switch off the router. What I'd like to to is run a cable outside for best cell reception and mount the ER703WP-4G-Outdoor there. Is there a way to utilize it as a backup WAN for the ER8411? I saw in another post that Omada does not support two gateways on the same site.

Can I still utilize the wifi portion to expand my interior wifi network outside, using my main ISP?