If you have been living in Hong Kong for a few years as a foreign person or an expat, you may realize that the place is a transient city. The expat community is certainly growing gradually, but it is also ever-changing. More than often you will find that some of the friends you have made 2 weeks ago or 2 years ago have left HK entirely. Some expats have stayed only in HK for a short while. This may turn into some frustration if one of your goals is to make long term friends. But when looking at it from a different point of view, you get the opportunities constantly meet new people (including both expats and local Hong Kong citizens).
The upside is that many foreigners who have relocated to Hong Kong would actually have found that they are benefited greatly from working and living in such a captivating city. After all, the city has always been an international hub.
But still as an entrepreneur of your own startup, you will want to get many business opportunities that are offered by mainland China and/or are available from the Southeast Asian region. The good part of it is that you may want to outsource to secretary or administrative work of your business to a one-stop-shop type of company secretary service agency, especially those ones who are making use of technologies such as a professionally designed and reliable company secretary software.
When you run your own business and got to the point where profits have become much larger than it was in the initial stages, you will be able to handle the relatively higher rental cost in relatively smaller spaces. Before coming to HK when you are living in expansive residential houses, you will immediately realize the major difference. Rental cost in HK (for your preferred expat area) is probably higher than in most places in Europe. The size of the apartment (you could get) is relatively smaller than you would have expected. Just as an example to demonstrate this fact, the total area in a typical three-bedroom apartment in a new HK building can mostly be equivalent to a small two-bedroom apartment in London.
Another thing may be higher pollution levels. Unfortunately, the atmosphere in Hong Kong may be rated among the most polluted in Southeast Asia. The main sources of pollution are emissions from vehicles and a relatively crowded city.