G'day Harry
The place to start for information on Converting Overseas Licences to enable you to fly in Australia is on the CASA web site here.
There are a lot of hoops to jump through!
You will need to:
get an ARN,
have a medical valid in Oz,
pass an English language test (yes, I know, it is possibly the only language you have but they still want to check that you can understand 'Strine', 'Chinglish' and ATC talk, etc.)
undertake an aeroplane flight review
CAO 20.11 gives the rules for flights over water and the carriage of life jackets and life rafts - and also other stuff.
In a single engine aircraft an approve life jacket is required for each occupant when the aircraft is outside gliding distance from land, and
a life raft is required if going more than 100miles over water.
I would suggest you go around the Gulf of Carpentaria rather than across all that water. There are quite a few interesting places to see around that coast and nearby anyway.
A good air law and operational procedures reference for VFR pilots is the VFR Flight Guide.
ERSA (En Route Supplement Australia) is a required document (each issue valid for 3 months only) which, amongst other things lists Registered, Certified and Military (and some other) airfields but there are a lot of local government and private strips not listed there - and you will probably want to visit many of those places. So you will need to get the AOPA airfield directory and/or the Country Airstrip Guide (for each state you visit) - they (CAGs) now have a web site too.
ERSA and other operational documents can be found and downloaded here.
Other publications you may find useful are ON TRACK and OUT-N-BACK.
A lot of pilots are now using EFBs, iPads or Tablets with OzRunways or AvPlan installed, to assist with flight planning and navigation.
Let us know where you plan to visit and the brains trust on this forum will very likely be able to assist with local knowledge, advice and alternative options.
Happy planning.
DWF