Forgive me please if these questions have been asked already.
In 2021 (in case Coronavirus goes away) I am planning to buy a Oneworld Explorer DONE ticket (4 continents).
I have a nice 16-segment routing with 42,281 miles. According to the oneworld tool, this routing seems to be allowed.

Is that routing really legal? ..-LHR-LAX-JFK-DFW-HNL-...

Somewhere I have read that the airline, operating the first segment, must issue the ticket. That would be Finnair.
I don't want Finnair to be the issueing airline, esp. because of their high ticketing service fees (esp. for changing flights). The ability the change the flights/days (not cities) is very important to me.

Can I still buy the Oneworld Explorer ticket with another airline, e.g. AA or BA?

Another question -> I have this routing: ...-HKG(72 hours)-NRT-PVG-HKG(12 hours)-DPS-..
As you can see I plan to travel via HKG twice, which is technically not allowed. However, I was just putting PVG-DPS into the oneworld tool. The tool returned flights via HKG (its the CX hub). However, is it allowed to extend the stay in HKG (the 2nd time) up to 23 hours? The oneworld tool would only return connections with 12, 13, or 14 hours. There are connections bookable on cathaypacific.com with 23 hours (if I search for a one-way ticket PVG-DPS), but the oneworld tool would not show them.