As other have said $75k is fine for 2 to live on but please factor in the time (few months) and expense to get registered as a teacher- skills assessment (a different one to the one for the visa!!) $110, registration $350ish and then you need Mandatory childprotection and first aid courses $110 and $60ish I think. I would also say you may struggle to get into supply/relief teaching without a car and of course she wouldnt be earning 75k straight away as wages differ as relief teacher and she probably wouldnt get full weeks work straight away.
Not trying to put a dampener on things just be realistic- in 6/12 months time she may well be on 75k but I would advise you need another source of income at first- but if you could turn your hand to most things there are defo jobs out here for you :) and she could probably get something whilst waiting for teacher assessment and registration to go through.
Good luck! x