The last thing I want to say is about Paris.
Before we go, I heard a lot that Paris is dangerous, a lot of pickpocket and robbery, never travel by MTR, etc. After my trip, I would say that Paris is still comparatively safe. In most of the place where tourists will go, it is fine. Of course, you still have your duty to take care of your belongings and keep your money safe. I am sure there are problems of pickpocket along the MTR lines, even the MTR broadcast tells you beware of them. There are also a lot of different people going to trick you for money, like endorsing whatever proposal, giving some invaluable hand string, etc., but this phenomenon happens not only in Paris, even someone may encounter the same in HK.
My observation may be subject to the recent attack in Paris. After the attack in November, all important buildings and tourist spot are heavily guarded by either police or even soldiers. I stay in Gare du Nord, which I was told many times by my friend that there is a thief's den. Now this train station is guarded by police outside and some soldiers patrolling inside. I can go out for dinner somewhere around Gare du Nord after 10:00pm.
Same as other spots. You have to pass 3 check points in order to get into Notra Dame. X-ray scan before entering any museum.
So it turns out more safe then you expect, though it is sad to have this kind of safety after attack.