Well, I think you already covered it quite well. A few more points:
- Generally speaking, a stopover is more than 24 hours, a transfer less. So depending on the situation you have to refer to stopover or transfer rules in the fare rules.
- A stopover always needs to be covered by the allowed routing (or maximum mileage). E.g. in your case, not all fares allow to travel to BNE via SYD.
- Stopovers attract fees (e.g. airport fees, security fees etc.). They may also attract higher fuel surcharges, depending on how they are calculated. Therefore, even a free stopover is usually not completely free.
- Most importantly: Stopovers are often difficult to book online, since online tools are not configured that way. So you need to contact the airline (by phone) or a book through a travel agent. Obviously both channels also attract some additional fees.
This is obviously not a complete list, but I hope it helps.