I am also from the Central Highlands, though this will be my first year trying tomatoes here. A lady with many years of gardening experience recently told me that tomatoes shouldn't be planted out here until Melbourne Cup day (5th November). It's simply too cold before then, especially overnight, and late frosts are still possible in October. For best results you should raise seedlings beside a sunny window or in a greenhouse in late September - early October, to plant out in early November. Or simply buy seedlings from a nursery - this is a much easier option but the number of varieties they sell is limited. I have researched on cold-tolerant varieties for this season and here are three that I am trying this year: Siberian, Stupice, and Swift. You may want to try to look for these varieties as they will probably be better adapted for this climate. Generally, any variety from Northern Europe is probably better to plant than typical Australian varieties, which are bred for hotter climates. Finally, make sure you are feeding them correctly. A high Nitrogen fertiliser is necessary early on, but once it puts on flowers you want to only feed it with one high in Phosphorus and Potassium. There are very few of these fertilisers that seem to be available at the big box stores (many have way too much N) but something like liquid potash or a 'flowers / bloom' labelled fertiliser should work. Make sure to include some organic fertiliser or organic compost when planting out your seeds / seedlings as well, so that your soil is not deficient in trace elements. I hope at least some of this advice helps and that you end up with a bumper crop this year. Tomatoes are probably harder to grow here than elsewhere but I have also been told there are less pest problems than up towards the tropics. Best of luck!

- Prometheus