I'm going to presume your math is correct, and that you can actually retroactively credit each ticket. Keep in mind that AA's status year is static, March - February the following year (so flights flown before then wouldn't count for status, I believe, since it's been so late in posting). Qantas is based on when you joined the program, you'd be better off posting in their forum asking about backdated status if that's what you're going for.

1: Yes, that is correct.
2: I don't believe so, I believe they give 1 months grace period for status posting.
3: That's a question better suited for the QF forum
4: Where are you based, where will you use the points to fly, and in what class? It's all subjective. AA points will be more readily available to be used on AA, QF on QF. QF also partners with EK, for example, if you fly them. QF is also a transfer partner of Amex and Capital One, so you can combine your miles there for redemptions, whereas AA does not have any transfer partners.