u/Electrical-Mix-2545

If i book an Alaska airline flight using Qantas points in economy, could I then upgrade on the Alaska website to first class using credit card?

I want to book a flight from SGN to TYO with Japan Airlines. This will only be a one way flight. If a do a multi city search SGN to TYO and then a week later TYO to ICN, the ticket is 3 times cheaper. If i do book the multi city flight and not take the 2nd flight, will there be any issues? Not sure is this matters but i do not live in the USA, i am using money leftover in my wallet from a cancelled flight.