There will be 2 challenges growing Vandas in Melbourne, Australia: Temperature and Moisture.
Temperature first: Most Vandas are warm growing orchids meaning minimum night time temps around 18C (65F). So you will need ot grow them wiht protection in winter and possibly even heat.
Secondly, moisture: Vandas are humidity lovers. In the US people grow them in humid houses or outdoors in warm humid parts of the country with their roots hanging bare and being bathed in mist as many as a few times a day. Others who don't have so many plants, soak the roots regularly. So if you grow them bare root, you'll need to figure out a way to mist or water them several times a day, probably less in the months when we have higher humidity.
I only have one Vanda-type orchid, an Ascocenda Gail Noyes. I have grown it in a clear plastic pot in large chunk bark. Because it is such an open mix, the water drains out quickly yet it stays humid in the pot. Even a week or so after I water i can still see humidity droplets or "steam" on the inside surface of the pot. I grow it inside my flat where the coldest winter night it gets is about 15C (60F). I have had good success with this way fo growing it. I have owned it almost a year and in that time it has grown about 2-3 new leaves and it has rebloomed; it's currently in flower.
Here is a pic of it when I bought it in bloom last year.
Now for a couple of questions:
1) What are your growing conditions/situations?
2) Specifically what kind of Vandas do you have?