So if anyone is interested I thought perhaps I should add my itinerary & basic plans. Of course given that I have no idea exactly how this will pan out, it's very possible that it will change but here it is for now.
26 August - London to Joburg / 02 September - Joburg to Perth / 02 October - Perth to Melbourne / 14 October - Sydney to Cairns / 20 November - Brisbane to Christchurch / 03 January - Auckland to Singapore / 20 May - Bangkok to London.
The current intention is to do a couple of days in Perth and then travel up to either Exmouth or Broome & back to Perth, take about 6 weeks to travel from Melbourne to Brisbane & take about 6 weeks to travel from Christchurch up to Auckland.
Once I hit Singapore I will have a lot more flexibility as my travels in SE Asia are all overland so I only need to get to Bangkok by the 19th of May. I intend to do 2 or 3 days in Singapore, about a week through Malaysia to Thailand where I intend to stay for about a month and then spend about 2 months in Vietnam, Cambodia & Laos & then back to Thailand again for another month hopefully to include Songkran (although that happens around 13/14/15th April & visas go for a month so haven't quite worked that out yet).
I am hoping not to need to change any flights (except maybe my last flight on the off chance I still have enough money left to last another month or so weather dependent) as Australasia is a little on the expensive side so that is what I have planned for at this point. Whether or not that changes remains to be seen :-)