I'll start this with the standard disclaimer that this is not financial advice (merely food for thought) and I am not a financial advisor nor have any relevant qualifications. I am sharing what I have found through my personal interest/research, in the hopes that it will give you ideas for your own research.
My first recommendation would be to invest your time in reading "Making Money Made Simple" by Noel Whittaker. You can buy it for around $25 or hire it from the library, but either way I found him great at explaining things.
If you're considering buying property to rent, I'd recommend you consider the following:
What demographic will live in the property? Working class? Students? Professionals?
Is it in a convenient location for the target demographic's work, public transport needs, infrastructure (shopping centers etc)?
Is it supported by a single industry (eg mining) which would mean your investment could plummet if that industry collapsed.
If another financial crisis were to hit, would you still be able to find tenants? Having two $200k houses could be better than having one $400k house for instance, as if the people renting the $400k house have to tighten their purse strings they might move to a $200k house. In general it's better to have more lower tier investment properties than a single more expensive one.
Also, consider the tax advantages available with investments. Any interest paid on money borrowed for investments is tax deductible, but money borrowed for your personal home is not tax deductible. This means if you have $400k debt spread between two properties, one investment and one your primary place of residence, you're better off (from a tax perspective) having most of your debt on the investment. This doesn't mean you have more debt, but just that you want to own as much of your personal home as possible (say $100k debt on your own home which you're paying off asap, before you start paying off the $300k on the investment)
Some others have mentioned offset accounts, and you've mentioned the possibility of two properties. If you go down the path of two properties, I'd suggest you consider getting a mortgage on each (with an offset account) with interest only repayments, and putting all of your spare cash (the $400k less deposits) into the offset accounts. This way if you want to use the money for personal reasons down the track you have easy access to it, you'll still have the ability to use the investment properties as a tax deduction, but you wont be paying interest on the investment mortgages for the money in the offset.
Hope this helps!