Exam

Dear Aaditya,
You need to first clear your aim what you actually want to do, that is, whether to clear GATE or UPSC. Yes, you have sufficient time to clear UPSC but for that, try to make your basics strong, like your GK level. Surround yourself with those who have great knowledge regarding interviews

Main Exam include 9 descriptive type papers:
1-Any language defined in constitution of India
2-english
3-essay
4-general study
5-general study
6-optional subject-1
7-optional subject-1
8-optional subject-2
9-optional subject-2
In this papers first two is optional paper means its marks are not considered but o

Admission in NIT, Hamirpur and other NITs,IIITs are given on the basis of the JEE Mains rank and after scoring a rank in JEE Mains you have to register for the JoSSA counseling on https://josaa.nic.in/webinfocms/public/view.aspx?page=46.
This year registration for counseling were open upto June 25,

Yes, you can upgrade it and don't worry for fees. The college will handle fees problem.

U can take direct admission in LIT Lucknow.

Depends on which branch you have opted.

MITS is not bad College. And if interested in Computers than go for IT. MITS facilities are also good. I prefer you to go for IT. YOU can use Shiksha college Predictor:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor