Thanks so much for your help Charles, really appreciate it.
Yeah, i've done steps 10-15, but this only displays your custom metadata editor page, as soon as you save your edits and close the editor you cannot see the new custom fields. The other links seems to be more about grabbing the xml metadata and doing some backend processing, rather than displaying it.
It's just a bit frustrating as the GitHub guide gets you 90% of the way there. I probably should have started off this thread by saying i'm very new to developing and using the SDK ... i was just trying to see if you could amend the metadata without years of development experience.
Anyway, I'd be very keen to hear from ESRI and if they are planning on updating or adding to the guides, or even better do a webinar.