Regarding the time for upgrades:
1- SOs will be SOs for a minimum of four years. Don't count on less, but it may be longer.
2- If you were to join today, you would have approximately 1700 seniority numbers ahead of you, waiting for a command. Even if the training department was to run at full speed, there wouldn't be any more than 100 command upgrades per year. Realistically, count on about 50-75 command upgrades per year. Do the math, someone joining the company today would see his command no sooner than about 17 yrs after joining, but more likely 22-25 years later. Some might retire before reaching an upgrade.
During that time, you will enjoy lesser conditions than any other expats in HK and have no chance of getting a base for a long time, as they are all full and whatever opening arise is given in seniority.
Sorry if I sound pessimistic, but that is simply how it is. Please do join if that is an exciting career prospect for you.