Please, need help with my Nighthawk R700P, Orbi AX400 Mesh Wi-fi, and AC1900 Wi-fi Extender setup

 My devices are:

1. AT&T Modem (ISP provider)

       ---2.4 GHz WIFI & 5 GHz WIFI operation both disabled. (someone said you can disable the router mode of the AT&T modem and just let it handle only "modem" stuff. is this true?)

1. Netgear Nighthawk R7000P

           --In Router Mode. WIFI antennas disabled. Used for Ethernet connection only. MU-MIMO disabled

3.Netgear Orbi AX4200 Tri-Band Mesh Wi-fi (1 router & 2 satellites)

        --In AP mode. for Wireless Connection upstairs. Have 1 unused.

4.Netgear AC1900 WIFI Extender

        --In AP mode. Use for downstairs WIFI extender. Connected to the Nighthawk router via ethernet cable.  Both 2.4Ghz and 5Ghz Network are enabled (Both have separate SSID, should i make the same?)

Issue:

1. Great connection at first. But Every 2 or 3 days, the Orbi WIFI connection will drop. Restarting the Nighthawk R7000P router fixes issue. But it will happen again.

                ---Is The Nighthawk R7000P better than using the ATT Modem as a router in this scenario? Do I just eliminate it so that I have one fewer device?

  ---In addition to disabling the wireless radio in advanced setup in the Nighthawk, do I also need to disable “Wireless Network (2.4Ghz b/g/gn) SSID Broadcast”?

  ---Or is there a setting I have to adjust to solve these connections drops, for example, "IP Passthrough", "DNZ", etc.?

1. I would like to replace the AC1900 WIFI Extender with 1 Orbi Satellite. But there is poor WIFI signal between Orbi router upstairs and 2nd Orbi satellite downstairs.

   ---Can I ethernet wire the downstairs Orbi to Orbi router and still use the downstairs Orbi as an Access Point for wifi?  Is this a good practice? Or must Orbi satellites be connected to the Orbi router wirelessly?