cleobella,
Thank you for your very kind words and I am glad that you found the review to be helpful for your planning.
Doing a private tour is very time efficient but expensive and so I understand your point. I don't feel that I am the final authority on the best day tour, but if I were planning a one day do-it-yourself tour of Hong Kong, I would visit the following:
1. Take the Star Ferry to Hong Kong Island and/or back. The ferry is not expensive and it is pretty quick. The Star Ferry has a long history associated with it. My mom rode the Star Ferry every day to school back in the 1940's. Star Ferry does offer harbor sightseeing cruises.
2. Visit Victoria Peak (Hong Kong Island) which gives you great views of the city and its harbor. I would pay the modest fee to ride the Peak Tram to the top and back. The next time I return, I want to go to the Peak at night to see the city lights. Admission to the Peak itself is free although the Peak Tram costs money (the alternative is walking up to the Peak for free). Once there, there are various free vantage points to get a view. Alternatively you can pay to get to the Sky Terrace 428 which has a viewing platform.
3. Go the the Wong Tai Sin Temple which is on the Kowloon side of Hong Kong. It is a shrine and a popular tourist attraction.
4. Visit the Ladies Market (Kowloon side) which is a very large flea market. It is fairly large and we liked it better than the Temple Street Night Market although the latter is worth visiting as well.
5. Finally make sure to visit a Chinese dim sum restaurant for lunch in Hong Kong. Although it was not invented there, Hong Kong is famous for its dim sum restaurants. It's worth trying if you would like an authentic Hong Kong dining experience.
It was also recommended to me by a local while we were in Hong Kong to book an Aqua Luna Victoria Harbour Cruise through Klook. Their recommendation was for the cruise as well as the website/app. It's not very expensive and there are some pretty cool options like a Dim Sum cruise in the middle of the day, an Afternoon Tea Cruise, an evening cruise, and a cruise during the Symphony of Lights which occurs every evening. We found out about it too late to book anything and so I had to be content with watching the boat cruise the harbor at night from our hotel room window. Next time we go to Hong Kong, I am definitely booking it. Klook is evidently a popular website/app to book sightseeing activities. I have no experience with it and cannot tell you what the attraction is.
If you have any more questions now or in the future, please do not hesitate to ask.
David