Wow, whwrw do we start. So many questions. I will try to address those I can one at a time
I assume by PAR you mean Paris. The airport used by Qantas flight QF17 is CDG (Charles de Gaulle). As you still have a few remaining segments, you could maximise your QF Status Credits by doing something like PER-MEL-SIN-CDG. PER-CDG on QF17 is going to earn you 60 SC's and 17,748 points as a QF WP. Going via MEL and SIN will leave your Australian trans-continental for the return and consume 3 sectors instead of one, but earn you 85 SC's and 24,492 points. Not bad for a few extra hours on planes.

Only other comment is that DFW-ANC is seasonal in northern summer only. The rest looks ok to me, but I will defer to the South American experts.
Good move to avoid BA/AA for QF points earning. You seem to have done your homework on the alternate flights.
see my comments above
Again, I will stand corrected by the open ticket experts. But my understanding is that the coupon will note the city pairs only and not a flight number or date. You can't just turn up at the airport and hope to board. You must change the open reservation to a confirmed reservation before flying, but that should not require the tickets to be re-issued, hence no additional charge.

But of course you run the risk of not finding any L inventory on the date you want to travel. Probably less of a problem for L, but can be a problem with D or A. Check the availability regularly and lock in the actual date as soon as you have the plans finalised.
As noted above, the ticket will not specifiy the actual flight, just the city pairs. Note that there may be some carriage restrictions on some codeshare and non-US airlines operating in north america. I am not sure about the CX JFK-VYR flight, but just check that it can be booked as an independent sector if you want to stopovefr at either JFK or YVR. I am not sure if it is like the QF107/108 LAX-JFK-LAX that can only be booked in conjunction with onward or inbound international carriage. Again, I am sure others will set us straight here.
An open dated ticket EZE-LAX will show just that on the ticket coupon. So the only way to use it is for a single flight number between those two cities (can include transit stops at intermediate cities). So no, you won't be able to change the open dates ticket to a confirmed reservation on anything other than a direct (single flight number) flight between EZE and LAX. You won't get that past the reservation agent, so it won't be up to the check-in agent to waive.
The ticket will be marked with an "x" in the first column showing that it is to be transfer only and not a stopover. So when you make the flight confirmation the agent should not allow you to reserve it such that LAX becomes a stopover. However, it is not unheard-of to have reservatoins agents miss that and permit the stopover. But don't rely on it. An alert check-in agent should pick up the error and seek to correct it.
I would not make that assumption. You have paid for an L class fare. If there is no L availability, you will most likely be refused. You should be able to be waitlisted for flights that don't show any L available.
It can be more risky. Lock in the dates as soon as you know when you will want to fly. Check the routes you intend to book over a period of time to see how L availability trends. Know the routes that are likely to sell out in L and those that are likely to be wide open in L up until the last day or so. Do your homework and research.
QF WP status will help with priority waitlisting. QF will be more likely to request availability from other airlines on your behalf. But it won't mean there is more L availability automatically.
Yes, you can use any OneWorld lounge on the you are departing on any OneWorld carrier. That includes the First Class lounges. Enjoy .