Ok, so everything's gathered together and I can fit it all into my 60 litre rucksack, with room to spare (taking the 60ltr because I want to get my monopod in it, something I can't do with a smaller one) and it's way below the 20kg limit (it's not even 10kilos), except my camera gear - three lenses, two bodies, CF cards and charger - and binoculars which will be coming in my carry on baggage (which weighs just 7kg, the limit).
Travel insurance is sorted, accommodation in Melbourne and the far north of Queensland (I have a couple of very long bus rides ahead of me!) is arranged and information gathered. This time in a fortnight I will be in the departure lounge at Heathrow T4. Bring it on!