That's doable, although traveling in Australia and New Zealand is likely to cost you substantially more than in Southeast Asia. You'll also have to really decide what your priorities are, particularly since Australia is a large country; and there's so much to see and do. The same goes for New Zealand. If money is an issue, perhaps you should spend only four months in Southeast Asia; then save some of the money that you would have spent there towards another trip, perhaps to South America. Sometimes you can't do it all on one trip, or you discover you really like a place and want to go back. For example, I so much liked Ethiopia that I returned the next year to spend another month there. Good luck with your planning.
[ Edit: Edited on 16-Feb-2015, at 11:09 by berner256 ]