IIT

B.Tech from IIT is better compared to M.Tech in IIT because in M.Tech, you may undergo specialisation. So, getting a job is comparatively less compared to B.Tech.

Clear your concepts and write test papers as much as you can and also, take help of you tube channels for better learning experiences.

No, its not true. You need not to pay extra other than your fees.

If you have will and meticulous planning to prepare for JEE and coping up with B.Tech studies, you can definitely crack JEE. There are lots of students who crack JEE while doing B.Tech in lower rank colleges. All the best!

B.Tech abroad is costly. If you can afford it, you can seek admission in foreign universities. Otherwise, it will helpful to take one year drop to prepare for JEE to do engineering degree from top engineering colleges like IITs, NITs and IIITs, etc.

For maths, go for Cengage and for physics, DC Pandey and HC Verma are good options. You can study chemistry from OP Tandon and NCERT.

If you have confidence that you could prepare well and qualify for SAT and JEE as well with good scores, only then choose dropping a year as if you don't get desired results after an year you'll be frustrated. So think wisely before you make a decision. Or else, there are many good private colleges as well where you can take admission.

No, IIT should not be your only option. There are other good colleges too. You can take admission in them as well.

PEC University-Chandigarh, Indian Institute of Space Technology, Anna University, Amity University and Manipal University are other good University for aeronautical or aerospace engineering. You may refer to the following link for a list of top aeronautical engineering degree colleges in India: https://www.shiksha.com/b-tech/ranking/top-aeronautical-engineering-colleges-in-india/49-2-0-0-0

You cannot get admission in IITs or NITs based on state board marks. In order to seek admission in IITs or NITs, you are advised to appear for JEE Mains and Advanced.