I've been BIABing in urn since 2009 and produce some often award winning beers. I personally wouldn't bother with any other system. I had been tempted to get a Grainfather but simply to produce clearer wort. However with a few tweaks I can now get this just as well using my trusty Crown urns and bags. I have a 40L and a recently acquired 20L that's a little terrier for competition and experimental brews.
Remember that BIAB or Grainfather or 3V mashing isn't brewing.
It's just wort production.
So you already have the processes nailed, it's just that you are replacing your wort stream with your own, not out of a tin
Lismore shop behind Aldi is ok for bits and bobs. They were doing sacks but ran into courier problems getting it in, not sure what the current situation is.
Gold Coast would be an excellent run to pick up your initial grain.
You'll need a mill, it will pay for itself fairly quickly if buying sacks.
I get my other stock such as yeasts, hops, spec grains, chemicals etc from Brewman or Craftbrewer and both deliver overnight Fastway.
If you are ever going into Brisbane, Craftbrewer is one of the main Australian suppliers and just 15 mins off the Gateway South and I grab a sack or two.
If going south, Country Brewer at Toormina or Brewman at Raymond Terrace are also just a loop off the M1. Brewman has a pick up cabinet so you can't go wrong, got my last two sacks from there on my Sydney trip last month.
edit:
Guide to All Grain Brewing using an urn,