Planning RED60 with XGS WAN failover

Hello together,

we have a use case at a customer and want to offer him RED60 and XGS126.
This is the planning

location outside                                                                                            central office
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                   RED60  WAN1   radiio line  -------------  radio line      XGS interface
            /       IP 10.0.0.2                                                                 IP 10.0.0.1                  \

branch office net                                                                                                            office network

                       failover                                                                                                         /
            \      RED60 WAN2   5Grouter  ------------  internet line     XGS Interface
                   DHCP from Router                                                    Internet IP-address

My questions are concerning:

a) the transfer network  for the radio line. Is it possible to use internal ip-addresses to connect the RED like this way ?
It is a little bit unusual, but it should work. on RED host WAN1=10.0.0.1

b) I had bad experiences with failover from WAN1 to WAN2, especially roll back to WAN1, if the line1 is available again.
Does anyone have good experience ?

Thanks for your answers :-)

regards

Anja