Comfortable 2-3 bedroom Apartment in mentioned areas (around 1,000 sq ft +) = Starts around 15K, so average say 20K
Live in Maid = Is pretty standard over here, around 3K a month
Gas and electricity = Upto 1K a month if you hammer the aircon
Telephone, internet and satellite TV = Go for NOW TV, they are the best, good package for around 450 HKD a month
Other stuff I dont know, so if you go for 50K, should easily cover and give you extra money to spend.
To get an idea of places, costs,
www.hongkonghomes.com and
www.gohome.com.hk
And SZ isnt that bad!
Good luck