Just a couple of things
I flew HNL-SYD last year in JQ business and had an excellent trip. The flight was 10 hours but all daylight, it was full service and the seats had good pitch and comfort. Highly recommend.
Re Qantas upgrades
As I remember JQ policy a year or two ago, you could apply for an upgrade Y to J using points plus pay providing you had purchased a full price fare in Y. The catch was that you didn't know whether your upgrade was sucessful until a short time before departure date. If you missed out you were stuck with your full price Y booking at a cost considerably more than the discount fare you could have bought. Is this still the case?
Qantas fares in any class other than "Sale" are now eligible for upgrading, however the points required will be higher for a "Saver" fare than for a more expensive "flexible" fare.
AA rewards.
Does AA have points as well as miles?
They are the same thing, basically.
How do you buy AA miles and what is the cost?
You can buy AA miles on the AA website, provided you've already been an AAdvantage member for more than 30 days. (So join now, it's free!) The cost from memory is USD$29.50 per 1000 miles, plus a $30 flat fee. However they run bonus mile promotions every few months which are worth waiting for. In a recent promotion, there were up to 60% bonus miles up for grabs.
Can AA miles be combined wih QF point to achieve a reward booking ?
Can you purchase a QF rewards seat using AA miles only?
Will AA miles be acceptable for a QF or other OW carrier SYD-LHR ?
AA miles and QF points are entirely separate things. However, QF points can be used to book an AA or other oneworld airline's flight and vice versa. So yes, you can purchase a QF reward seat using AA miles. It will be subject to availability and whatever AA charges for the seat. QF don't really have anything to do with it in this case, other than being the operating airline. For any flight within Australia & NZ, AA charge 10K miles for an economy seat or 17.5K for business, plus taxes (but crucially, no fuel surcharge).
Yes, you should also be able to use AA miles for any oneworld airline between SYD and LHR, for example, however there are two key things to be aware of. Firstly, award seats are subject to limited availability so you really need to plan ahead. You may also not be able to find any seats on certain days. Flexibility is key. Secondly, many AA partner airlines don't show when you search on AA.com. You'll need to call AAdvantage to get access to these seats.
I would highly recommend you have a look at the Knowledge Centre, and in particular this section on buying AAdvantage miles:
Login Required — The Australian Frequent Flyer Knowledge Centre