Was India the reason for future expansion of the British Empire?
It is certainly accurate to say that much of the expansion of the British Empire after the 1750s was largely due to factors related to India. It is somewhat subjective to say whether "almost all" of the expansion was due to India.
Not all of the expansion of the empire was based on these factors. For example, the colonization of Australia had very little to do with India. It was driven at first by the need for a place to put convicts and then by wool and gold and other valuable things that could be gotten from Australia. Similarly, much of the expansion in Africa was only tangentially related to India. It is difficult to argue, for example, that the taking of Rhodesia was connected to India more than it was to the mineral wealth of that area.
But much of British expansion was tied to protecting India or to gaining markets in which to sell products from India. The acquisition of the Cape Colony was driven largely by a desire to protect trade around the cape. British involvement in Egypt and Sudan was driven by the need to protect the Suez Canal. Much of the "Great Game" with Russia was driven by the need to protect India. The acquisition of Hong Kong was driven by the desire to sell Indian opium to China.
In these ways, a great deal of the expansion of the British Empire was due to factors related to India. Whether this reached the level of "almost all" is a subjective matter.