Rizzo welcome the forum! Where in Australia are you?
I would be more inclined to run the QS8s as side surrounds and not worry about a rear channel unless you are able to keep the seating away from the rear wall by a couple of feet, in which case you could then run a 7.1 system, your room is plenty big enough for a 7.1 system or just 5.1 with side surrounds. The QS 8s give a very enveloping sound and they can be mounted in the rear or to the sides as desired but the usual way is to have them to the sides and slightly to the rear of the seating area, but as I have said this isn't set in stone.
So far as a receiver, pick one in the price range and with the features that you like. Onkyo, Yamaha, Denon, Harmon Kardon are all very common HT receivers, well around here anyway. You could even go with a Sherwood Newcastle from Axiom as the S/N's are very good HT receivers as well. I had an older Denon 1804 and I recently upgraded to the 3808 which is a very good bang for the buck with network connectivty for audio streaming and firmware updates.
Just ask any questions and I am sure someone on this forum will be able to answer.
