It is perfectly legal to have a part time DH. she just need to be PR. I have had part time helper for 7 years and it is totally legal. She is HK Chinese and we pay her 80 bucks an hour (because she has been with us a long time, the going rate is more 60-70HKD/ hour).
If you work on the island do not get a car for work. parking on the island is very expensive. it does not make any sense unless you live in the NT and want a car for the weekend.
flats, you can get good accommodation (600+ Sqf flat in modern building with swimming poll.. For anywhere between 8k and 18k depending on whether u pick somewhere in the NT, Kowloon or HK island).
50k as a single 26 years old is good (even in banking you would not be making that much more unless you were working for one of the big Us bank or some boutique that pay nicely).
All in all it sounds like a good deal and if I were you, I would take it (for info am in banking, been here 7 years and lived in all three areas: HK, Kowloon and NT. All have + and - but as a single, 26 years old and if I were to work in Central/HK island I would pick a place in Tin Hau, North Point, Taikoo or on the other side at Kennedy Town. close to work, the happening places and yet affordable and 'spacious'. you could get some place in Wanchai...but it would be rather small).