>> 1) Will my wife who will be on dependent's VISA be able to look for work in HK?
She will have to apply for permission to work. Dependants of folks on employment visas are not longer given automagic permissions to work.
>> 2) Housing wise I am looking at service apartments as an option for a start. Will HKD 10K a month be sufficient for a 1 bedroom apartment in town and near MTR? If not what will be a reasonable housing allowance?
10K may be reasonable -- check the rates in our serviced apartment listings on
http://www.geoexpat.com/resources/Ho...ents/index.php
(Yeah, I'm sure the local trolls will recommend other sites for serviced apartments, we recommend a broker we know works well, because they give us commissions!

)
A lot would depend on where your office is.
>> 3) Any recommendation on reliable relocation agencies that I can talk to for advise?
We've heard good things about AsianTigers (
http://www.asiantigers-hongkong.com/ ) and Santa Fe (
http://www.santaferelo.com/ecs/index.jsp ). Asian Tigers helped us with a complex office move and Santa Fe sponsors a lot of events at the American Women's Association where we're active.
The cost of living is surprising cheaper than Singapore if you consider the +++ taxes that get levied on everything. Housing is a bit more expensive so that is the major plus.
I've generally found Singapore a bit more expensive than HK.
>> HKD 850K annual package(includes any tax benefit + "CPF" similar contribution from employer) but excluding housing allowance reasonable?
Yes, it is reasonable in absolute terms. However, there are always other soft and emotional costs related to moves. At the end of the day, if you're happy with it ... thats what matters right?