IIT

Hello Saurabh,
Well, cutoff seems to vary every year so it's quite tough to predict but however, if you score around 110-120 in advance you will get any IITs.
All the best.

IITs have the best facilities, faculties, brand image, international reputation, placement records and alumni network which no private university except BITS-Pilani can match. In addition, you will compete with best students of India which will bring best out of you in academics. Probability of succeeding as a IITian is highest in India and abroad. Therefore, you may prefer IITs over private universities.

You have to qualify the JEE Mains and Advanced entrance exam and also qualify HSC board exam with 75%.

All branch choices depend on your interest and all branches are good if you have a good knowledge about it.

You may refer to the following link for tips on clearing JEE: https://www.shiksha.com/b-tech/exams/jee-mains/preparation-tips

Total seats in IITs are 11 (4 in IIT Powai and 7 in IIT Guwahati ) for B.Design for SC category students. You have lesser probability of getting admission in IITs for B.Design.

Check out the eligibility predictor for JEE Advance :
https://www.resonance.ac.in/answer-key-solutions/JEE-Main/2017/jee-main-2017-eligibility-predictor.php

Go through books of IIT-JEE books and previous year question papers.

If you are diploma candidates then you have to start your engineering with first year for IITs by qualifying the JEE Mains and Advance exam.