Chennai

Yes, to get admission in Chennai campus, you need to attend the counselling at the Chennai campus only. For all the campuses, you need to attend the counselling at Chennai campus only.
For NCR and Haryana campuses, you may go to the respective colleges.

NITs will not offer Diploma, they only offer Bachelor's degree and Master's degree. Try for some Hyderabad Universities or college like CBIT, VASAVI etc.

Hello,
Greetings from Shiksha!
CBIT is very good for you as it is having a good record, try for it. It also has a good placement, if you have an opportunity go for it. Hope your doubts are clear, good luck!

Your rank will be around 20000 so you may get the main campus of SRM University. You can easily get other campuses with this rank.
The branches at main campus may not be good for your rank. You may get chemical engineering, civil engineering, mechatronics, etc. but at the other campuses you can get all the courses.

Hi Dear,
Here is an article by Shiksha authors about top engineering colleges along with their rankings, fee structure and total seats. Just apply the filter to get desired results.
https://www.shiksha.com/b-tech/ranking/top-engineering-colleges-in-india/44-2-0-0-0

VIT University, Vellore campus is really better than Chennai campus. The hostels are good and the food also, as they are very essential. It offers better education and placements with high salary packages.

SRM University-Chennai, KTR Campus is better than Sikkim Manipal University. So, you can go for SRM University. It has better placements and offers better education also. You can go for Sikkim Manipal University, if you don't get SRM University.

Both are really same in all factors. They are highly reputed institutions and offer good education and placements. So, you can prefer any one of these two colleges.
But, PSG Coimbatore is widely preferred to MIT-Chennai, even though both are equal. MIT is Government College, but PSG is a private college.

Hello Akash,
You may refer the links below for the list of top aeronautical engineering colleges in Chennai:
1) https://www.shiksha.com/b-tech/colleges/b-tech-in-aeronautical-engineering-colleges-chennai
2) https://www.shiksha.com/b-tech/ranking/top-aeronautical-engineering-colleges-in-chennai/49-2-0-64-0