This gives context to money in this time period. We know it is a large sum based on their reactions, obviously, but clarifies each person's situation based on their reaction as well. It gives Sherlock and Watson context to how well off Miss Morstan is, and it gives us, the reader, a base for Sherlock and Watson's financial situation as well.

Here is some segregation of cultures, I believe it is key to understanding more about 18th century customs and regulations. They are in a shabby neighborhood which is predominantly Indian, this could be intentional or just writing what was true at the time.

Sort of a little foreshadowing here, with Watson's emotions being displayed flamboyantly.

This is a classic Sherlock quote, it explains his intelligence in a way that fits Sherlock's attitude and presence. This is a really good way to have believable characters, they say things you would expect them to say.

It is interesting how much sarcasm is used in this story, it highlights the beliefs and the culture of the time in a way that we in the future can interpret similarly.

It is actually a little comical how nonchalant this seems, though for historical context, this was actually quite common, most of the poverty that was exhibited during this time involved addiction to opiates or other now-illegal drugs.