Answered this with the help of Customer Services. Thankfully the issue I was having was unrelated to a mesh WiFi/modem mode. My kit hadn't been activated yet!
I called up Customer Services as I was getting Account Error CS1011 when managing to get connected through ethernet or WiFi. They advised the kit hadn't yet been activated and resolved this.
Since this was sorted the box connects up as easily as any other device such as a FireStick/AppleTV and is working very well!