In regard to Hildebrand's address, I think his main residence was at 26, Upper Bedford Place. He and his children were listed there during the 1871, 1881 and 1891 censuses and when he gave a deposition before the United States Supreme Court he gave his address as Upper Bedford Place. In addition, his practice was in the city at 150 Leadenhall Place.
But he did have connections to Walthamstow. He attended the Forest School there and he had a cousin, the Rev. Tullie Cornthwaite, who, from sometime around 1840? was affiliated with the Forest School and had a house in Walthamstow called The Forest. Hildebrand was quite close to him. Tullie was a noted botanist who published books and treatises and when he died in 1879 he bequeathed some of his possessions and his extensive herb garden to Hildebrand. In the 1871 census, Tullie is recorded as living at an address which is called Forest Rise.
Since I live in the US I am not too well informed about the local geography. I assume you are more knowledgeable about the locale.
Hildebrand's father was Vicar of a parish called Forest Gate in East Ham, Essex and the family lived there until the children moved away. I suspect that that place was not far from Walthamstow.
Perhaps you can sort through some of this information and come up with a clearer picture.