Well, for anyone else interested in trying the RAK solution to having your own gateway set up, it seems very easy so far, and I've got to say I'm impressed.
Thanks so much to Jeremy for the heads up on how simple this solution is.
The package was received on tuesday, but I had stuff on. So, I only got started yesterday.. I did all the pi setup stuff (mostly straightforward! I love it when FOSS stuff just works and doesn't require hours of googling out of date threads to reassemble basic information that should just exist!) and registered my device for the auto config system by adding a new file in the special github repository as requested.
When I got in to my office this morning my device file had been merged to the device auto config repository, and was already downloaded to my pi.
Then just registered the device on TTN console, reset the RAK831 board, and it seems I'm up.
Now to get the tracker module setup for AU, and get out and about with it.