You will have plenty of time to convert your licence, becoming a citizen here takes around 7 years. How do you plan to support yourself in Brazil during that time? There is a fast track of roughly 3 years for certain nationalities, but Australian isn't one of them.
To answer your questions
1. Conversion isn't difficult, but would depend very much on where you plan to live. Some ANAC offices are more helpful than others, and some seem to take great delight in making life as tough as possible.
2. As aenobre says, the airlines are more likely to be laying people off than hiring in the short term. However as you are looking at the market 7-8 years from now accurate predictions are more difficult. My impression is that the industry has now rationalized itself and we won't see any major changes unless the Government really introduces incentives to boost regional aviation.
3. You probably won't get another pilot job here, there are thousands of unemployed pilots willing to work under appalling conditions for nothing except hours. The aviation English market no longer exists as a viable career choice. I taught for two years at a specialized language school in the run up to the requirement, now I have a few private students preparing for retests or interviews in the Middle East.
We have (or used to have) a member here who was trying to do what you are planning and he had some high level contacts within the industry. He eventually gave up and is now happily flying in Guyana, I think. Search for posts by flyingswiss in the Latin America sub forum to get an idea of what is in store for you.
Hope that helps a little, although I expect it isn't quite what you wanted to read.
Good luck, and feel free to PM me if you have questions that you would rather not post on an open forum.