Will try to answer some of your many questions.
SO's live in HKG...you can now join as DEFO or Freighter FO if you have the experience and so could, theoretically, never live in HKG during your career(depending on what type you are on and basings availability). Basings are allocated on rank and then DoJ. So if you got a base as an FO great...you can stay on it until your seniority would get you a command basing. But if you are from NA it gets complicated as there are currently no right to left upgrades on pax fleet 744...but I think there is on freigher 744?
Complicated huh...simple answer to a complicated issue...you could probably spend almost your entire CX career not living in HKG.
Unofficially...you have to take the SO to FO upgrade(can't think why you wouldn't want to). They don't like it when FOs refuse command but it has happened many times (due kids schooling in home country etc).
Relief commander=relief FO...about 12-18months after you are upgraded to FO(assuming no failed upgrade!). On ULR 4 man crew, the RC sits with the SO for his shift. Captain and other FO do takeoff/landing. RC gives a great lifestyle but sucks as a job...you hardly ever do takeoffs/landings.
Career progression is based on DoJ AND assessment. So if you were delayed becoming an FO for some reason, that does not penalise you in your race to be upgraded to CN.
Usually when guys/gals are talking about their 4th go they are talking about upgrade from JFO to full FO. I haven't heard of anyone ever getting 4 shots at command...I think there has been the occasional 3rd go...not sure. Once you are assessed by a command review board, you are made Cat A or B...B means "naughty boy politically, or we don't think you are ready" so you do more time as an FO. Cat A means ready to give the course a go. If you fail command course you get made Cat C. If you fail again they usually make you cat D. Cat C means you will get another go in a year or three...cat D means never!
Clear as mud?