Architecture

You can go through the following link:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

Admission is through counselling based on the rank obtained in JEE Mains. For further details regarding thsi course please refer to the link provided below:
https://www.shiksha.com/architecture-planning/course/b-arch-school-of-planning-and-architecture-ip-estate-delhi-73566

You should have scored more than 75% in your 12th exams and your rank should be around 5000 in B.Arch to get NIT.

You stand a good chance. You will most probably get the seat. All the best for your future.

Yes, you can take admission in design college on the basis of JEE Mains paper 2. Since NATA paper has a huge weightage of drawing, abstract and aesthetic sensibility, it is given more importance than any other exams. On the other hand JEE has been producing brilliant architects for as long as 40 years now. Both the exams have an equal importance in the field of design. You can either appear for one of them or both. Appearing for both, however, will give you the upper hand.

UPSEE 2018 College Predictor
Use your UPSEE 2018 rank to see where you can get admission at the link provided below:
See the courses, colleges & rounds you may crack
The result is based on admissions data of UPSEE 2017
Get resources & insights on colleges & courses
https://www.shiksha.com/b-tech/resources/upsee-college-predictor.

https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor
Please go to the college predictor link that I am sharing here. You will know all details here.
Good luck.

Your rank is too good. You will definitely get the best NIT colleges. Check college predictor which is based on last year cutoff for assuring which colleges you are eligible for.
Good luck.