Hi Van
$400-500k will buy you properties in Sydney, including units closer into the city in well regarded growth suburbs, in small blocks (higher land value content) and with some pretty decent yields at the moment. Freestanding housing will be found further out (try north and southwest) but still good value and rents rising in most demand areas of Sydney. If you do decide to buy in Sydney, we can begin a whole new post on the areas if you like
I'd agree with the others here in that you need to do further research and be aware that middlemen such as these investment companies are only going to be showing you limited stock, with which they have affiliations with the developers. They are salesmen as such and, unlike independent buyers agents, are not going to be recommending properties unless they make a commission. Nothing wrong with this, as this is the way selling agents work, but be aware that their comments are going to be biased and totally focussed on getting you, as buyer, to commit to their product. That's all.
These companies generally only show you new stock as they can't make money from established property, unless you're paying them a finders fee, in which case they'd be advertising themselves as independent buyers agents. It may be worthwhile investigating Brisbane BA's if you feel you'd like to go down this path, and cover the entire market, not just a small restricted portion of it. Though you pay a search fee, it's often paid for itself and more with the experience and negotiating skills of a good BA. After all, BA's are out there on a regular basis, buying for people, and have the huge benefit of local knowledge on their side as well.
Also concur with the others that you need to know your recent sales prices so that you're sure you're not overpaying. Check out postcode 12mth sales from companies such as homepriceguide, residex or RPData for most up to date accurate info, or ask a REA pal for latest sales info if they subscribe to RPData. Being able to justify your offer is vital if you're to get the property for the fairest price in today's market.
From what I've heard, Brisbane certainly is in the upwards swing of the cycle but that's not always the best time to buy either. Look at what happened to Sydney buyers in 2003 who have lost selling since then- the market can become overheated and due for a correction years down the track. It's a myth that real estate never goes down, trust me
Keep asking questions here, read as much as you can and be as fully informed as possible before you commit to any purchase. Best of luck with it all!!