I didn't catch 2 things earlier, 1. you are female, 2. you are new at this,
http://chinasurvival...ngers-of-china/
HK is relatively safe compare to other places. I never actually lived/worked there long term, so Mandy is probably the one to ask for that. You can never be too careful sometimes. If you aren't from a big city(are you?), HK can still be a daunting experience.
In terms of cost, HK is one of those places like Taipei where everything is so convenient that I usually don't know where my money goes until the end of the month. A few coffees here, a few 7-11 trips there, and it all adds up. There is a huge temptation to eat out all the time, which can cost a fortune unless you find out about decent spots with local prices.
In terms of packing, don't bring your whole wardrobe + closet. It's a tempting option for new expats sometimes. HK is fairly humid, while a lot of regions in US are fairly dry, so you might want to find out if your favourite skirt/jacket will survive the trip. Sweating can be problematic for some people. You might want to pack things that will wick away moisture. Layering is probably key. Anyway, just bring essentials, and you can probably buy (the rest) some very nice clothes in HK on sale for very good prices compared to home.
Things are more crowded in a lot of Asian Cities, especially places like HK. I don't know how big your room is, but some of my friends had trouble adjusting to their much smaller lodging. And make sure whoever roommate they set you up with is tolerable. Looking for a place on your own in a foreign land is not a fun experience.
If you have never taught Chinese students, it can be a bit of a daunting experience. Kindergarten teachers usually face a lot of pressure from Chinese parents. That is one of the reason I stopped teaching young children.
Anyway, good luck and have fun. Keep us in touch.