Well, the opening shots of the film suggest that Ching Pak House, in the Cheung Ching Estate on Tsing Yi, is the main location for the film and Stanley Fung's flat. This, however, is a fib. When Eric Tsang first shows up and is let into the apartments by Sandra Ng and Clorinda Chan, the Kai Fai House signage is clearly visible. It also makes sense, when you take into account that almost all other locations are in the Choi Wan Estate too. There isn't a Street View of the entrance to the block, but this Street View image should give you a hint of what you're looking at...
