Reserving DONE without paying yet
 

I am seeking to generate an itinerary for a DONE so that I can starting applying for visas for the trip.

I don't want to pay for the DONE at this stage in case the trip doesn't go ahead for some reason.

What is the best way to generate an itinerary without paying? I know I can book through a travel agent, but will an airline let me book and itinerary, but not ticket that this stage?

I am based in Australia and when I use the online tool it directs through Qantas who give me this price:

Fare component: $14,799 AUD
Taxes and Carrier Surcharges: $1427.

Is there still a differential so that it is cheaper booking through American Airlines?
If so, can you email the proposed itinerary to them so you don't have to be on the phone for ages giving them the itinerary dates and segments?

the xONEx fares are based on where you start flying on that ticket. Theoretically the cost should be the same independently of the issuing airline, but each has different policies on the application of "taxes/airline fees" for each flight segment. Typically the airline flying the first segment or first international segment would be the ticketing airline. But many (AA/QR) will likely be willing to ticket if they market one of the longer intercontinental segments.
An inexpensive ticket to Colombo (CMB) to start would at current exchange rates reduce the base ticket DONE6 cost to AUD 11538 and permit you to have more stopovers in the South Pacific region.

Happy wandering
Fred

Technically, if you book 29+ days before departure of the first flight, you should be able to hold the reservation until 25 days before departure of the first flight without payment if the message "OSI YY OW RTW" is correctly inserted in the PNR. Unfortunately, this is theoretical only, and some airlines are not able to read this message correctly. Nevertheless, if you book far ahead, you should be able to at least hold it for a while.

I think you are entitled to a full refund if you provide evidence of refused visa. Please fact check me. :)

For what countries do you need visas? It might be easier just to book some fully refundable RTs - even just in the local area - instead of the DONE to apply.

It's not quite that simple. For starters, it depends on which country's passport you carry. OP says that he's from Australia. Easy enough, if time consuming, to check online.