Not sure if that helps at all, but I currently have this:
https://www.amazon.com/gp/product/B00A121WN6
This is connected to my modem on one end, and to my PC on the other.
My receiver is connected directly to the modem.
All you need is a basic $20 network switch such as this one on amazon https://www.amazon.com/Ethernet-Splitter-Optimization-Unmanaged-TL-SG108/dp/B00A121WN6/
If I'm understanding your needs, you are ok with using the Starlink router and its wifi. But you've added the ethernet adapter and simply need more wired connections?
If that is correct, you don't need another router. You need a simple network switch similar to this.
You would plug the ethernet cable from the Starlink ethernet adapter to one of the port. Then connect your other devices to one of the remaining open ports.
If I've misunderstood, I apologize.
So you remove the FIOS router and plug the ethernet cable that was going to it into the "Globe" icon on the bottom of your google wifi. You get just a cheap 8 port hub at BestBuy/Walmart/Amazon, etc. and plug a cable between one of the ports on the hub and the other port on the google wifi Puck. Then the devices that were plugged into the Fios router plug into that. A lot of people will say get a switch but for the size of a home network a hub will do fine. The only difference between a switch and a hub is a switch knows which devices are on it and only forwards traffic for those devices. A hub is whats known as a "dumb" device and rebroadcast all packets sent to it over all ports. Unless you have more than about 15 or 20 ports a hub is more than adequate.
For the piHole it is a simple single board computer called a Raspberry Pi that blocks advertisements and known malware websites by acting as the DNS server for your network.
Please just buy one of these for $18 and avoid the hassle
https://www.amazon.com/gp/product/B00A121WN6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
My system is
Modem -> Google Wifi -> switch - > (multiple computers/tv/game systems) -> switch -> (more computers) -> Google Wifi puck #2
And this works great
Ideally you want to disable the "router" part of their "gateway" (disable routing, NAT, and DHCP, and the wifi AP) and use it like a modem and connect the "WAN" port of your router to it. Sometimes this is called "bridge mode"
I've found this article describing how to use it:
https://www.xfinity.com/support/articles/wireless-gateway-enable-disable-bridge-mode
The other option is to use a switch, but all you need is a basic Ethernet switch. I would not waste the ERX on that duty, but instead pick up a dedicated Ethernet switch - you can get one with 8 ports for like $20 on Amazon.
Either of these would work fine:
i have a G3100 with 2 G3200 in different parts of my home. i have the below switch connected to one of the G3200 and it works great
https://www.amazon.com/gp/product/B00A121WN6/ref=ppx_yo_dt_b_asin_title_o06_s01?ie=UTF8&psc=1