If things are complicated, it is always better to discuss with your travel agent. In general:
* If you have to fly L on certain segments and the rest on D, it will still be a DCIRxx.
* I don't think AKL-CHC-SYD will have any problem.
* Mileage is calculated on all connections. Although I have not done that, I believe the miles on land segments are also counted.
* You can take KA.

Note: There is no direct OW flight between Beijing and Shanghai (all airports). You would probably flying PEK-NRT-PVG or PEK-HKG-PVG. However, I don't know if the intermediate point (NRT or HKG) is considered a stopever. (I flew PEK-HKG-PVG once before on the same day, but the segment was marked as 'O' because I originally did not intend to fly on the same day anyway. Also I had to re-check-in in HKG even though both segments were on KA.) You may consider taking a train from Beijing to Shanghai. You can depart in the evening and arrive early the next morning.