stat in stature Riddles

A man who lives on the tenth floor takes the elevator down to the first floor every morning and goes to work. In the evening, when he comes back, on a rainy day, or if there are other people in the elevator, he goes to his floor directly. Otherwise, he goes to the seventh floor and walks up three flights of stairs to his apartment. Why?

I am a word of five letters. Take away my first and I am the name of what adorns the estate of many of the nobility of England. Take away my first and second, and I am the name of a place where all the world was once congregated. Take away my last, and I am the name of a beautiful mineral. Take away my two last, and I am the name of a fashionable place of resort. I am small in stature but capable of doing a great deal of mischief, as I once did in London in the year 1666. What word am I?