Dude - you are 18 and the amount of maturity you have shown in this post is already commendable. I always think there are two ways to look at life -
You are already planning to do 1. In addition to JEE prep, I'd say start working out - at your age, testosterone is off the roof - you will be able to see muscle gains quickly. You will gain a lot of discipline and self confidence in the process. A good body and a sound mind with a passion for quantum physics, man you'd be unstoppable.