Best to see after dark from Kowloon side of Hong Kong. However so called "light show" is just average.
I think 3 days in each place is good. In Seoul - try and get a hotel near the Myeongdong area. I stayed at Hotel Venue G. It was within 30 min walking distance to most of the interesting places like Insadol, the Palaces... More
I think 3 days in each place is good. In Seoul - try and get a hotel near the Myeongdong area. I stayed at Hotel Venue G. It was within 30 min walking distance to most of the interesting places like Insadol, the Palaces, the temples, Tapgol park, the shopping areas, Money museum etc. The metro stations were within 5 min walking distance. For Hong Kong, I preferred Hong Kong Island over Kowloon. I stayed in Harbour Grand hotel in North Point. It was a pricey hotel as I was with my family. I am sure you can obtain a more economically priced hotel in the Causeway Bay area. This is a lively place with lots of eating places, bars and shops. Give yourself one day to visit Kowloon. The star ferry runs frequent services between Hong Kong and Kowloon. In Kowloon you will find Kowloon Park, Nathan and Chatham Roads, the avenue of stars, promenade (to watch the light show), Jade market, many shops and eating places, museums. Spend another day going to Macau on the early morning Turbojet ferry and returning in the evening. Best to book tickets in advance and online - so that you get cheap tickets. Otherwise, you will pay for more expensive tickets if you go to the ferry terminal to buy tickets as the cheap ones are all sold out. Spend another day in Lantau Island. Take the yellow metro line to Tung Chung. From here take the cable car to Ngong Ping Village to see the Buddha and the monastery. From here take a bus to Tai O fishing village - and return to Tung Chung by bus. If you need any other information, let me know.