The only problem is you are not allow buy a one-way ticket to Australia if you are holding a tourist visa. What I'm going to do is buy a cheapest ticket to Auckland (should be the cheapest) from budget airline. But if you are going to buy a return ticket, then it's alright!
If you want to travel overseas while your temporary partner category visa application is being considered, you will need to apply for a specific bridging visa to allow you to travel overseas and then return to Australia. To be granted such a bridging visa, you will have to provide reasons for the travel and then the travel component of the visa will be tailored accordingly.