Please do not waste your money. I have to travel to China with my job. I have been to all the main cities, and I would never go back if I had the choice.
Hong Kong is nothing like main land China. It's a country in itself. It has a massive expat community and definitely worth a visit. But no more than a few days.
The good thing about Hong Kong is you can fly to much nicer destinations, especially Thailand and Singapore.
If I were you, I'd forget about China and head to Thailand. The food is far better (Chinese food in china is nothing like you'd get in your local takeaway), the people a nicer, and it's far more beautiful.
If however you like rude people. Lots of smog. Soulless cities and disgusting food, go to China!
The food in China is likely to be 10x better than what you'd get from your local takeaway and 1000x more varied. Not to mention a helluva lot cheaper.
And since when has a large expat community been a tourist draw?
I'll give you the rudeness though. Manners are a little different over there.