That depends on what you expect from your time and money. Checkout my website to see what your money will realistically get you.
I have been lucky enough to travel to almost one third of all the countries on earth. Yet no other part of the world has had such an impact on me a here.
research as much as you can about what is there and decide what you want. Decide how much time you have and focus on that
India is a whole subcontinent so there is no clear answer. However, the peak season for tourism as a whole is between November and February.