Stop in Soho for a coffee or wine and to people-watch. Chinatown is early in the tour but has an array of options for food and drink on the way.
The architecture photography works best in daytime hours.
Take only the equipment you can carry. A lens in the range of 18 - 55mm or 18 - 105mm is suitable. I don't recommend a tripod as the footpaths are too narrow.
Be aware that pickpockets work in all areas of the city, but especially where there are crowds. Keep your gear close and be aware of your surroundings at all times. When photographing people, either ask permission first or be discreet. Anyone in a public location can be photographed, but if you are going to be very obvious, please obtain their permission. If you intend to use the photograph commercially, you must have their written consent via a signed model release form.