JEE Main

The best government. College of India Offering astronomy and astrophysics are:
IIST KERELA, IISC - BANGALORE, IISER - branches, Indian Institute of astrophysics (the best in the country).
https://www.iiap.res.in/
and IUAP (Inter-University Centre for Astronomy and Astrophysics) Pune.
Best of luck.

Since NITs are tough, among NIT-Patna, Bhopal, Jaipur, Kozhikode and Calicut, try for each with only home state quota. Else, go for Private Universities offering B.Arch and B.Planning.

You'll get NITs such as
1-National Institute of Technology
Tiruchirappalli
2- National Institute of Technology (Warangal)
3- Motilal Nehru National Institute of Technology

Sorry, you will not be eligible for top architecture colleges. Though you have good rank, B.Arch and B.Planning are two single branches with limited seats and colleges across the country. Try for autonomous colleges of your state with home state or try for private colleges and universities.
Best of luck.

I would suggest you to try for the top NIT's in the order: Trichy, Rourkela, Nagpur, Jaipur, Bhopal, Patna and Hamirpur. You'll definitely get into top 5 of these. Also, try for the SPAs as well: SPA Vijayawada, Delhi and Bhopal.
Best of luck.

With the predictor, it only not shows the last year stored data with the college seats but also shows you the related and the best-suited options with your other exams, letting you know about colleges beyond what you are expecting. Jadavpur University though accepts WBJEE and you need to be in top 500 to be able to get admission into it.
Best of luck.

Yes, it is expected to see a change in the Mains pattern but not at a certain extent as government knows better than what should be the rate students can accept the change and they will plan the change accordingly. Moreover, no one can exactly predict what would be the scenario in Mains-2019 as it is the first time, I would advise continuing the same pattern and studies as if any change occurs, it'll be minute.
Best of luck.

Kindly mention the college you are enquiring for as different colleges have different closing rankings with them.
Best of luck.

I would suggest you to again acknowledge your rank as it's not likely to have such a huge difference in the category and General Rankings. Moreover, till then, use our college predictor to better explore the opportunities:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=6375912

For admissions in M.P colleges, you need only JEE Mains marks. For admissions in UP colleges, you need to give UPSEE only for state government universities.
For admission in DU, the admission is on the basis of CBSE marks (for political and human resource courses), or on the basis of separate entrance test and JEE Mains marks as well. They have a separate number of seats for separate exams.
Hope it helps.