You have ( ----> representing an Ethernet cable):
ISP (Frontier) === Fiber ===> [Garage FTB] === coax ===> [Modem/Router] ~~~~> wireless devices and -----> wired network devices
And the requirement is to add an Access Point.
ISP (Frontier) === Fiber ===> [Garage FTB] === coax ===> [Modem/Router] ~~~~> wireless devices and -----> wired network devices with one LAN port being -----> moca #1 ===> Coax ==== house coax cables ====> moca #2 ------> Access Point -----> wired/ ~~~ >wireless network devices.
Correct? If not, feel free to edit and correct my line diagram.
What are you planning to use for the Access Point: make, model? What other devices are to be added via the Access Point?
Who has full admin rights to the existing modem/router and other network devices?
One thing that must be avoided is the creation of a network loop: Device A connected to Device B connected to Device C connected to Device D connected to Device A again.
Actually any sort of loop in the overall network connections.
Edit my line diagram and add more details.
Depending on the details, there may be other options.