Setting up Orbi backhaul

Modem Combo Units: https://community.netgear.com/t5/Cable-Modems-Routers/What-s-the-Difference-Between-a-Cable-Modem-and-Cable-Modem/m-p/1864698#M21950
This would be a double NAT (two router) condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
https://kb.netgear.com/30187/How-to-fix-issues-with-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the Orbi router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop

Be sure you connect any RBS wired to the back of the RBR directly or thru a switch. You can't connect the RBR and RBS in parallel to a switch infront of the RBR as the status reporting of the RBS will not work on the RBR. Any wired RBS needs to be serially connected behind the RBR.

https://kb.netgear.com/000051205/What-is-Ethernet-backhaul-and-how-do-I-set-it-up-on-my-Orbi-WiFi-System

Yes if you can directly connect the RBS to the back of the RBR, you can hang a switch of the back of the wired RBS. 

I would disable Daisy Chain on the RBR as well. 

30 feet is recommended in between RBR and RBS to begin with depending upon building materials when wirelessly connected. https://kb.netgear.com/000036466/How-far-should-I-place-my-Orbi-satellite-from-my-Orbi-router