I used to cycle in London, and I wouldn't do it to commute here. Even seeing cyclists on the country roads on the weekend makes me nervous! The biggest problem is that unlike in Europe, where everyone probably cycles, in HK no one behind the wheels of a vehicle will be familiar with being a cyclist.
I suggest you consider maybe living in a more cycle-friendly area in the New Territories or even outlying island, where a little cycle ride could be part of your commute to public transportation. In this areas there will be places to lock up your bike. It's true, though, actual government-built cycle paths are pathetic for speed, and when you see how locals generally cycle, you'll be glad they're slowed down, hah.
Transporting a bike on the public transportation can be another nightmare, so if you live closer to the areas where you want to train on the weekends, it would be much easier. Foldable bikes are popular here (granted, not what you're thinking), and could be an option for your regular commuting.
This is another good bicycle shop: https://www.facebook.com/FriendlyBicycleShop/
By the way, in the more bicycle-friendly residential areas, there are a lot of advertisements for used high quality bikes at very cheap prices. I guess people buy it with lofty ideas of hitting the road every weekend, and then end up not and getting tired of it taking up space in their apartments. You may have a look. Bikes do get terribly rusty here very quickly, and need constant oil.
I sadly had to leave my beloved bike back in the UK. But it was the right decision after all.