Hi there, @Manny1984.
You are free to use a Third Party modem instead of the Optus supplied one. If you decide not to use the modem we supply, the support we can provide may be limited. You can find the settings required to manually configure equipment to the Optus network in Home Broadband technical settings.
Depending on the size of your house, a mesh system may work better to ensure you get a strong signal in all parts of your house.
I'm sure others with more experience in using Mesh networks or who are familiar with the Netgear Nighthawk modem models will be able to chime in here.
If you have any other questions, let us know!
I'm not too familiar with these types of set-ups however going from other threads in YesCrowd, if you want to keep VoIP functionality, the Optus supplied modem still needs to be part of the setup.
I'd recommend checking this particular thread as a starting point on how to configure your setup so you can keep VoIP functionality.
For deciding on a type of Mesh system to use, it's probably best to get recommendations from the Manufacturer's support teams to see what would be most suitable for your home or engaging with tech sales consultants if visiting a retailer that sells Mesh systems.
I'm afraid Optus don't sell modems that only do just VoIP. You can check our Support Page for currently supplied and approved NBN modems.
You can configure your current Optus modem by logging into the modem settings and switching WiFi off to avoid interference with your BYO modem's WiFi signal so that the Optus supplied modem only serves the VoIP functionality.
With FTTC, the NBN box is the modem so you don't have to worry about "VDL / ADSL" as they are modem related, so any router will do for your situation.
To use the Optus VoIP service you will need to plug the 5366TN into whatever new router get and do some configuration on the new router to get the phone working.
If your main/only issue with your current setup is just the wifi range, then you might consider just getting a wifi range extender instead.