The areas you mentioned are good, I'd just be a little concerned about the price. Guessing these are new builds if they are in/around Glenvale? 3x2 or 4x2??
For the money you're talking ($600k) you would almost have enough to buy a pre-existing house on a big block (under 250k - albeit in an older part of town) and build your own set of duplexes on the back (350k+ for low block duplexes) and have one more income stream coming in.
Bit of work involved, but worth it long term.
Otherwise, just look for the house on the big block initially and go from there. Or if you don't want the hastle of the development, why not look at two houses for $500k and spend the rest of the cash renovating them to increase cash flow.
Take this advice with a grain of salt, I have no idea of your investing situation or goals... I guess this is what I'd do if I were in your shoes.