Assam

You can take mass communication as this course has better career opportunities ahead. You will get good opportunities for you after pursuing this.
Good luck.

NIT Agartala is the Second Best after Silchar in NE states. Thus as per my view I would suggest you to go for SILCHAR -NIT is the best in terms of Placement
Infrastructure, Environment. Etc. Thus this purely on my views and as per this factor.

As per your question, you should go for NIT-Silchar. It has good placements and infrastructure as per other NIT in NE. NIT has a good environment and infrastructure and with fair placement records, among the other NIT in Northeast and after NIT Silchar comes the second that is NIT Agartala.

As you are interested in sports, you can apply for B.P.Ed course.

Don Bosco University of Guwahati and the fee structure is 3.79 Lacs and they accept CAT percentile.

If your B.Ed is done from a reputed institute, then it is valid all over India.

Yes, there is strong possibility of getting a good NIT for your category score. You should be calm and choose the list if colleges wisely and go till last round of counseling it will be helpful. You can check out this link for prediction of colleges. https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor.