I have been getting mine from this Fengshui shop (Ground Floor) of Burlington Plaza (next to SIN MIN Plaza, Rochor).
To activate them, you need to put red thread or red ribbon. Usually we use red thread.
As to the number of coins required.. really depends on the specific need. The experts will advise.
How and Where to place them.. again, depending what we wish to address.
Maybe let me site some examples here.
At the back of the door (inside of the house), string three ancient coins, this will bring good wealth to the owners. In addition, a bell at the front of the door... with red thread too.
The other is to place three ancient coins with red thread (to activiate them) under the door mat. THis helps to promote wealth.
Some people may say it is superstitious.. however, if one feel that one is enjoying the benefits or addressing some issues (having a peace of mind).. simple act like this.. wouldn't harm, isn't not?
As you can see, alot of the businessmen.. banks.. corporates are also practicing Fengshui. So, believe it or not?
As said, I have been reading Fengshui books for the past decade. My crazy platonic brother actually holding a Fengshui Diploma from Beijing. He is a CEO of a MNC..by the way. Hence I tease him that he can be a Fengshui Shifu for his 2nd carerer.
It's our interest. It's very interesting!!