I am a new member of this community and seem to hope that finally all my questions will be answered.

To start, I am currently studying in 2nd year of Bachelor in Mechanical Engineering at Jadavpur University, Kolkata, India. I want to change my stream to Theoretical Physics after the completion of undergrad degree. I am currently self-studying a bit, e.g. Feynman lectures, OCW MIT course, don't know what else to do.

So what should I do now? I know I'll have to do research work and/or summer intern. Where and how should I apply for in India? Also I need help regarding my studies, e.g. which books/materials to follow etc.
Another important thing is that where'll I get letters of recommendation? Since my profs are Mechanical Engineers, will their recommendation be of any value to the grad schools?
Do I even stand a chance to get admitted to any of the top 20 schools, with scholarship? I badly need good advices. With thnx in advance, dibyo.