Where can I find a list of the major developments that helped London grow and expand before the 20th century?

Answer 1

The number one factor was the railways, which allowed the development of new suburbs.

The creation of new, unified administrative structures was also important - as soon as the Metropolitan Board of Works was created it commissioned Bazalgette to develop a new system of severage and fresh water supply.

Answer 2

There are many excellent books about the history of London. One of the best is Peter Ackroyd's 'London, A Biography'. get it from your local library. it will tell you everything (nearly) you want to know.