Mobile Broadband Netgear Aircard AC785 dongle failover with Netgear Orbi, OpenDNS, DNSOMATIC,

Hi

I am considering buying the Orbi as a possible solution to my house.
(3 story victorian house c. 3,500 sqft with various dead spots, annoyingly in the kitchen, and nothing in the garden).

I have some concerns currently which stop my purchasing it.

I have no doubt of the performance, but for my setup to work I need the following.

1) USB Mobile Broadband
My Netgear Aircard AC785 mobile broadband to be able to plug in via the USB socket to act as failover broadband (or infact if I decide in the future to do away with my fibre broadband provider)

2) DDNS - DNSOMATIC.COM
It looks like currently there is only dyndns.org and noip.com ddns as an option.

I need to use dnsomatic.com as this can update my dyndns account and my opendns account at the same time.

Those are the two critical things for me that would prevent me buying it.

I would in addition like to see usb 3 for printing and fileshare.

I am also not sure what happens if you then need a 3rd Orbi, its not clear ( to me at least) how this communicates to base and/or the satellite, maybe someone in the know could clear that up for me that would be great.

I currently have a ReadyNAS for critical files, but I also use a usb drive for kids things like films.

Any help here would be greatly appreciated.

Ben