Thanks for the reply!
I believe it's easy to get SFP specs to match ONT's specs.
From an educational point of view how is it possible to configure pfSense to act like this (or any other) ONT?
As I mentioned, that ONT is very likely the demarcation point between you and the ISP. It will have functions such as status monitoring, configuration and more that your ISP expects to be there. You can't replicate that with pfSense or anything else. It's part of the ISPs network and you just can't remove it. Also, in many areas, regulations require a demark point, so you're not allowed to remove it. In my work, I have set up many customers on fibre. There was always a piece of equipment, owned by the carrier or ISP that was the demark. There were even 2, where one carrier was providing service for another. There might also be VLANs or MPLS involved. That box is an essential part of your connection. Don't remove it.