Presumably you're doing OW Explorer. Nothing wrong with your itinerary so far except that the CX trip planner doesn't show Broome-Darwin. You can do it via PER, of course.

If you're looking to maximize miles, you'd want to use all 4 segments perhaps as PER-Broome-PER-SYD-DRW-DPS. DRW-DPS is between regions and doesn't count as a segment in either.

You're allowed to purchase two more segments if you want to accumulate still more miles and paying for the privilege is worth it to you.

Stopover duration is of no concern. You have a year to finish the trip, and can stay in one place most of the year, if you want to.

If you're not aware of the Cathay downloadable trip planner, grab it from their site; it's a useful tool for trip planning, although it doesn't say anything about OWE rules. <http://www.tarom.net/ba/explorer_jan_03.pdf> looks to be a decent summary of rules.