Hi mate,
Welcome to the forums. I'm also from Adelaide 😃
These are questions that are very hard for anyone else to answer because it all comes down to your priorities in life.
If you are looking to buy a house soon, the best thing isn't to chuck the 100K into the market, as markets can drop just as you need the money. Best to decide whether you want a house, how many kids you plan to have, and how big it needs to be, before deciding on what to do with the cash.
JLCollinsnh.com has a good article on why renting is better than buying. Not sure i agree with him, you may however. He also has a great stock investment series, if you havent read it.
if you can find a better interest rate on the savings while deciding, no reason why you wouldnt do that.
VAS & VGS is a pretty common combination here, with maybe a bit of emerging markets in there. People also do a few things to diversify more as the Aust market is pretty concentrated. Maybe look at the EX20 etf, or some of the LICs such as WAM.
Personally i bought a house in inner west a couple years before finding MMM. Planning to pay it off ASAP and then boost the investing more.
Whether you go the housing route over the stock investing is totally up to your preferences, but i would suggest that there is no hurry, and plenty more to read before deciding. Good luck 😃