Your problem will be that it is well-nigh impossible to get an employment visa for bartending work. So unless you have the right to work in Hong Kong by some other route then forget it - there is basically no illegal employment in this field.

And no, there is very little tipping - most bars include a 10% service charge in the bill and that is what people tend to pay, perhaps plus a few coins. Whether that reaches the staff varies from bar to bar.

Basic salary for bar staff is around HK$7-8000 per month.