Is it possible/ legal for the groom to have a best woman rather than man? How would you go about arranging it? Does anyone special have to be notified?

I don't know about marriage customs in Hong Kong but here in the states the title of "best man" holds no legal meaning whatsoever. It is merely a "responsibility" bestowed upon a close friend or family member. He provides emotional support for the groom and often times holds on to the rings.

Traditionally the "best man" is male. But if the groom has a special female that is close to him she certainly can be the one to stand by his side. Even brides now have male friends or female friends walk them down the aisle instead of their fathers.

Absolutely! There is no 'rule' anywhere that says your best man has to be just that, a man. There is no special planning. There is no one to alert. The main reason for having attendants at your wedding is that these people are your friends and family that are saying, "we support your marriage and are happy for you." They are your witness to your marriage. You'll need them to sign your marriage license as well.

A girlfriend of mine had a dozen or so attendants at her wedding, half were girls and half were guys. Doesn't matter if it's guys or girls standing at your side...the only thing that matters is that it is your friends up there supporting you. Hope that helps.

The honor attendants at a wedding have only social and emotional, not legal, significance...I had Brian stand up with me when I married...and I fully expect to stand up for him if he ever weds...you can have anyone you want as your chief attendant.
The reason that we usually see attendants of the same sex is that until fairly recently, one's close freinds were usually of the same sex....now that you best friend is as likely as not to be of the opposite sex, the custom for choosing attendants is changing to meet that.