A few things to note about HK:
1. A taxi is often times not worth it.
2. Take a look at the MTR map. 95% of all things you will want to see are usually within 10-15 minutes of a stop.
3. MTR can often be faster than a taxi. The time between trains is generally only a few minutes. The distance between stations is generally around <5 mins.
4. Going around HK is easy because you can get by using English.
5. If taking the ferry to Macau, make sure you're at the right port. Macau has it own currency, but will take HKD at par. HKD is more valuable by the slightest amount IIRC (10 HKD = 10.3 MOP). No need to carry extra currencies.
6. Octopus card is great for travel, can be used to purchase things. It's essentially a preloaded debit card.
7. There is a bit of walking involved, everyone moves fast. Don't be surprised if an 80 year old granny shoves past you because you're "slow".
http://www.mtr.com.hk/en/customer/se...ystem_map.html
I personally have relatives on the light blue line, but train from there to the other lines is about 10-15 minutes. But IF I were to go there and stay in a hotel, Mong Kok, Yau ma Tei and Prince Edward are very central. Higher end, Tsim Tsa Tsui or Central/Admiralty. Kowloon Tong/Sham Shui po are probably very good value and still very close to those locations. I'll mention locations to see and cheaper souvenirs in a different post.