Hi Luke,
Where abouts are you located in Australia? 1 brood box should be fine, all my hives are single brood with 2 supers. I still get the occasional swarm but this behaviour stopped a couple of months ago. My advice for swarm control is exactly what you are suggesting. Rotating honey and capped brood frames up into an additional super, you shouldn’t need a 2nd brood box if you are located in a temperate zone of Australia.
There is a post on this method here =>
http://forum.honeyflow.com/t/comb-on-bottom-of-flow-hive/8835/8