1. Have you looked at a map to get to India?
2. I imagine traveling by car would be very expensive given the duties crossing over the countries. This is what you need to bring a private car into Laos:
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Into China:
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I'm not going to do your research for you.
3. You have a few routes to get to India from Thailand:
A. Thailand/Myanmar (Burma)/ India. Problem: Myanmar is in the middle of a civil war, and they have always been very difficult to get visas.
B. Thailand/ Laos/ China/ India. You get to avoid Myanmar, however China and India do not have the best relationship for now.
Remember, if you rent a car in Thailand, you'd have to figure out some way to bring it back.