I would say young babies are easier to move than older children, as although you will miss their nct/baby group buddies (and I moved overseas (not to HK) when DD1 was 16 months old) actually emotionally it is less upsetting for the children.
We're in HK now, and there are a few MNers here also...although perhaps everyone's been away enjoying travel in Asia over Christmas, hence the silence.
There's a web site called geoexpat and take a look at sassy mama to get an idea of what is out there. You won't need to worry about schools yet (!!!) and will be able to enjoy live-in help which, although not necessarily the uncomplicated joy it sounds, does mean you have more freedom than in UK.
Lots of choice about where to live, especially without having to decide based on where you get a school place. To give you an idea mid-levels for a feel of the city, southside for a more beach lifestyle, new territories for more space...there are outlying islands with expat communities...there is somewhere for everyone depending on your priorities and budget.
Living space will most probably be smaller than UK, rent is eye-watering. Personal experience for me is three/four times London. Health care is excellent...public hospital a&e lacks the queues and drunks of UK, and if you have insurance then private healthcare is dream like.
Life is expensive...petrol, cars, groceries, clothes...all much more than UK, and although tax is less, HK is far far more expensive than UK but it is safe. It is clean.
Expats are friendly...everyone knows what it feels like to be new, so people very open to meeting for a coffee.
We won't live here forever, but it is a great experience.