NIT

My friend got 187 marks in JEE Mains 2017, which I think are approximately equal to your score in JEE Mains 2018. He was not able to make it to IIIT-Bangalore. Last year's cutoff was 190 marks and cutoff marks of IIIT-Bangalore is increasing every year. Therefore, there are less chances for you to get into it. But, do not worry, there are endless chances and opportunities waiting for you ahead. Best of Luck.

Firstly, I would like to congratulate you upon your success. Now coming to your question since allotment of colleges are done on the basis of general rank so you might not be fulfilling the criteria for allotment of seat so that is the reason you might not be able to grab CSE in top 5 NIT.

Talking about best private architecture colleges in India, here is my list:
HZU (Himgiri Zee University), Dehradun
Aayojan School of Architecture
ACN College of Management and Engineering
Acharyas NRV School of Architecture
Adhiyamaan College of Engineering
Out of the colleges mentioned above, I think Himgiri Zee University as one of the best university for pursuing architecture. Their department of architecture offers an extensive study of design, planning and architecture. They provide the students with exposure to boost their confidence in the respective fields.

Please go to the college predictor link I am sharing here to know about the college you can get.
Link:https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor.Good luck.

Yes, you'll get some NITs for sure. For your possibilities in IIT, mention your Advanced score.

Yes, you have performed well and you have high chances to get NITs. You may also get your home state NIT. All the best.

Yes, and congratulations.

Yes, you can. Go for the counseling and wait for the last round. Till then, lock a seat at the first college what you will get and then wait for your turn. There may be a delay but you will get a good NIT. And if you don't get an NIT, don't feel sad. There are other government colleges also which would be a good choice.

IIEST, Shibpur is better as it holds 17th rank in All India Engineering colleges by MHRD. From my personal experience NIT Andhra Pradesh is not a good opinion.