I lived in London for over 30 years, it was a very exciting city to be in.
Notting Hill and Belgravia are where extremely wealthy people live, as are Chelsea, and almost anywhere west of the centre.
Rubbish collections are at night, because of the traffic levels during the day, so all the rubbish is put out by the businesses at the end of their day, normally around 1730-1800.
British people are generally very introverted, especially the ones who live in the south and in London, they hate talking to strangers, so they will make sure, especially on the tube, that they are reading something, so they don't have to make eye contact with anyone. That said, most people are actually very nice, and they're happy to take photos for you if ask, or will help if you need help (like if you're having trouble negotiating what ticket you need to go places).
Yes, Public Transport ticketing is an unholy mess, and seems to be designed to trap tourists into paying way more than they should, as unless you register a credit card, or phone now I believe, you will have to put money on an oyster card, which will have an unused portion at the end, which most people can't be bothered to claim back. Individual journey tickets are eye-wateringly expensive, as are the daily travelcards.
There is little traffic now in the touristy bits, because they have basically banned cars from many routes and paved it over. As a result, the city is dying, from the centre outwards, because, as you can imagine, although it's great for tourists, it's no good for anyone who wants to get there to work, run a business there which needs deliveries, or for anyone living there because movement is now so restricted and expensive, the remaining traffic routes are very clogged. There has been quite a migration away from London, compared to what it used to be like, the city has gone very quiet, last time I was there in rush hour, I was very shocked.
Glad you enjoyed it, but you need more than a few days to see it properly, stay longer next time. :)