Agree with the above on getting around... taxi drivers don't speak English (with very very rare exceptions) and the concept of addresses doesn't work in the same way as it does in the rest of the world. It is by far easier to get around by the subway system, which is very efficient, easy to use, and labelled in English. It is also a fairly easy place to walk around, but obviously much too big to do everything that way.

One "difficulty" for a visitor to Tokyo is that it really doesn't have a single "centre" or "downtown" in the sense that most big cities do - it is more a collection of many different "centres" so it is unlikely that you could find a hotel base within a few minutes of everywhere you want to be.

In terms of costs, Tokyo is more expensive than either HK or Singapore. Between those two it depends very much on what you are buying. Since you appear to be coming from the UK, then HK has got substantially cheaper in the last few months since the HK$ is tied to the US$ (as is Singapore's in a looser way). And those cost indexes are based on a certain style of expat living, including larges houses and school fees, so they are not really meaningful for the tourist (or indeed for people who choose not to live in the traditional expat style).