Sounds like a great ride to help others. What is the cause? You are on the right path. I would look for a more upright position. This could be achieved by getting a bar riser and one that moves the bar back. I've not done this so I cannot give specific advice. However, you can look here http://www.twistedthrottle.com/shop-...le-1050-05?p=1
There are probably other sources in Australia that will be more economical for shipping, etc.
Depending on your dimensions, you can look to lower your pegs to give you more leg room. (Although, I would hate to do that as it reduces corner clearance).
Get some kind of throttle lock that allows you to cruise without having to hold the throttle. Here are some types of throttle locks/cruise controls http://www.aerostich.com/a-to-b-util...ruise-controls
I'd look for an aftermarket seat. Like Sargent, Corbin or even better look to have it custom built to your body. I don't know how well the air cushions work but that may be a more economical choice that will do just as well. Others may chime in.
Also, as you already know you are going to be riding 833 km or 517 mi a day. That's a lot to start at. You should be getting ready now by working up to that slowly.
Get some kind of underpants that has padding. Many just get regular cycle shorts.
Some people have found that their bike burns oil which is not normally a problem because we are riding a few 100 miles at a time and with time in between. When you are riding day after day, check your oil every day. I would bring extra oil. I know of one guy that seized his engine in a similar endeavor because he did not think to check his oil. Bring chain lube as well.
Make sure you have good gear that allows you to adapt to the weather. I personally love my Aerostich.
Get yourself a platypus or other apparatus that allows you to stay hydrated.
I also found this link that gives some other tips from The Iron Butt Association
Good luck and keep us informed of your progress.