Hey,
I know quite a bit about France - the culture and people. Hope I can help you out a bit. I have studied French for 8 years, worked, gone on exchanges to various places in France, and lived with French families. Also, I have a part-time job as a Engligh tutorand I tutor native French people. So re your questions. Of course, the caveat to all these answers is that it does depend on the person, but generally this rings true to most French people.
1. Indeed, the French are more 熱情. Kissing on both cheeks when you meet a new person is good manners, so you should do this. If you are scared to do this to a new person, what I find is that they normally they will initiate this and you just go along with it.
2. Best to learn some basic French: just shows them that you are interested in their ulture and willing to find out more about them.
3. The French love wine and cheese - can expect these on the dinner table, e.g. if you are going to visit her family or something. Sometimes they have cheese as a dessert. If you think the taste is too strong, just decline politely.
4. As for the presents, I think bringing them something unique from HK or something that represents the Chinese culture is a great idea, especially since you say your friend likes Chinese culture. The Chinese box is a fantastic suggestion because it is so pratical. Alternatively, you can get one of those Chinese fans with paintings and art work on it? Or maybe a piece of jewellery like jade? Or some Chinese artwork in general?
5. Generally, there isn't much to living with French people - they are just like normal people! Just joke with them, tell them about yourself, ask them about themselves etc. The younger generation is not majorly different from HK young people - there are all types of people with different personalities - just like you would expect anywhere. Except generally, they tend to like to go out to party more than Asian people - although if your friend doesn't drink, then she might not go out as much. They still listen to generally the same music, e.g. Lady gaga, Rihannna.
Just be polite and be yourself and I'm sure you will make a good impression.
Hope you have fun and enjoyable trip!
