Yes, due to the plenty of rainfall and high summer temperature, you may feel muggy in HK. However, it will not cause any problem to your travel. Just take it easy!

Yeah, that's true. You should also not go hiking at this stage in the year - it's too dam hot still and thunderstorms could prove a real hazard if you're stuck on some random isolated mountain high up and away from everyone and everything.
The visibility should be pretty nice still then - the SW monsoon should stay with you for your whole stay. This means you could have some great views of the place. Have a nice stay.