Cellular backup to home internet

I would like to setup a cellular failover for my home internet.  I currently have ATT fiber (unfortunately Google fiber not available in my area), who currently only provides cell backup for Small Business (which cost 3-4x what I pay for residential for same speed).  The current ATT modem is not dual LAN and does not have/support battery backup. The whole purpose is to ensure I have internet connection should internet/power go out.  With all that said, I'm assuming I will need to get a dual LAN modem (recommendations appreciated) and was considering the Nighthawk M1 mobile router for my cellular connection (hopefully compatible with ATT, otherwise I will need to use another provider, again any recommendations appreciated).  To add more to the mix, I currently use Orbi mesh network to support all wifi devices as I'm trying to get close to 5K sq ft covered with multiple rooms.  I would like to confirm if I am on the right track with my plan or any potential obsticales I may face.  

Thank you in advance for any and all suggestions/info.

Cheers,
Steven