Just a small one from my most recent experience, the OW tool didn't work on an otherwise valid itinerary without selecting a preferred carrier in the top right on the page with all of the flights listed. I couldn't get mine without choosing CX which isn't actually what I wanted except the first 2 segments, however it wouldn't even entertain me otherwise. That also forced me to use CX on my final segment which also I didn't want since JL flies it directly, but c'est la vie, it's a few hours for a massage in the Pier and to get tanked at the bar. In my limited experience with CX so far and reading others' reports, best to have it lined up first via the OW site then make final adjustments vs. trying to find a CX phone agent to do it all.

BTW, looks like your proposed itinerary will force you to ticket on JL, are you sure you really want that? They have a ticketing fee and also a service fee, even for changes that would otherwise be free. Seems you have leftover segments, why not go with CX via HKG and ticket with them? You'll add a bit in airport taxes / fees since HKG likes to add a bit of a pounding these days but if you end up doing a bit of otherwise free changes, might be worthwhile.