I have also been looking around HK for the last three months with a budget similar to the one mentioned above. Beaches, villages, country walks, great local and foreign food, community spirit, no cars, except a cute little ambulance, beautiful trip to work (rather than crammed in into a steel tube) and fresh air.
Really, for any comparable on HK Island you need $10k a month atleast and battle the traffic. The only vague downside I can see is that if you want to go out at night, you might have to stay out, although I have heard there are some other water-taxi-like options, but i'd rather sek siu ye or sauna+massage and catch the first ferry back.
As for ferry reliability, I defer to the experts, but I have asked a few and this is the first I have ever heard of it.....but also, thanks for keep the rents low.
And now I can happily say that I am the proud tenant of a Lamma apartment, moving in this week!