I think I felt the same way as you at that time, so I will help you answer in the name of an experienced person.
1. After I took Luohu to Shenzhen, I went directly to the hotel in Luohu District. I took a bus to Luohu Port (wharf), crossed an overpass, entered a building and followed the crowd. You have to get your passport ready, and you can take the subway after two passes. It's convenient to buy an Octopus at the subway entrance.
I live in Causeway Bay, next to Times Square. It is very convenient to take the subway. When you get out of the subway, you have to change trains when you get out of Times Square. However, the subway is very convenient. Generally, if you buy a map, there will be subway lines on it. It only takes a few minutes to understand it.
3. Buses are not expensive. We only need 9 yuan from Causeway Bay to Repulse Bay, but the subway will be more convenient and faster than the bus. If you buy Octopus, you can go anywhere by subway.
I bought Disney tickets from Taobao. I didn't go to Ocean Park, so it shouldn't be much cheaper. The main thing is that you need to find a store with high credit to avoid trouble.
Subway is the most convenient way to clear customs.
We went for four days, and it cost 400 Hong Kong dollars for two people to take the subway.
Went to Repulse Bay, Taiping Mountain, Victoria Harbour, Xiejie and Disney.