Yes, it is a good idea to do shopping in HK around the Christmas in every Dec. Usually, the sales season will start from early Dec.

Yes, most of them are original one, such as Nike and Adas. But, please go to these shops affirmed by HK Government.

At the Fa Yuen Street, you could purchase these sport brands at very discounted price. Or, you could go to the Citygate Outlets located in Tung Chung.