IIT

Hello Anmol,
Your analysis is on target. You have scored quite well without any coaching and I am sure with coaching your rank would improve substantially. It's therefore a good decision to take break for one year for concentrated studies.

Firstly, you can solve NCERT (physics) then you can solve HC Verma and you are fully prepared for boards and for IIT, you can solve the objective questions of physics.

Follow NCERT, solve as many questions as you can, solve questions banks and solve previous year questions.
You may refer to other books also like RD Sharma for maths, HC Verma for physics, etc.
Good luck.

Super 30 is the best for the same.

Hard work, smart work, dedication, guidance, are the most important thing. First of all, finish your 12th syllabus first then revise concept of 11th as burden of board exam will not be there if you will follow this method. You can take help of private tuition or coaching centres. Take advise from your school teachers as they know you better and also from seniors who have cleared IIT exam.

It will depend on you if you confirm about that you can qualify JEE next year so you can wait for next year, otherwise don't waste your time anywhere to preparing for IIT.

No, it requires speed to answer and is at Mains level.