I believe you may not have gotten an answer to you post as it contains some irrelevant info and doesn't cut to the chase your requirements from the RPi and things like budget, experience with RPis/Linux, if it's a hobby or learning curve.
What does concern me (with what I think you are trying to do - although a couple of my questions in the other thread are still unanswered!).... is that if you find the Zyxel's GUI challenging, then unless there is a specific reason you want to monitor using DSLstats... why make things over complicated?
You said you already monitored the old Netgear modem using Routerstats on a laptop. So why not just make things easy for yourself and run DSLstats on your Windows Laptop?
I don't want to discourage you from dabbling & learning with a Raspberry Pi if that was your intention. But most of us here run DSLstats on Windows (or Linux) PC's. Those that run from an RPi usually do so because they don't have a desktop/laptop that they want to leave switched on 24/7. eg one of our regs uses a RPi in an otherwise totally wireless iOS network (iPads & iPhones only).
Aside from the fact of having to build and set up the RPi, you will then have to do so some configuration to get DSLstats running on it.
Whereas DSLstats works practically 'straight out of the box' if you run it on a Windows machine.