Engineering Entrance Exam

Hello Ritesh,
You may use the JEE main college predictor given below for knowing the colleges that you can get:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor
For previous year stats, refer:
http://josaa.nic.in/Result2016/result/OpeningClosingRank.aspx
You may consider the previous year stats as accurate, as they vary every year. You can get NIT Hamirpur, Jamshedpur, Agartala, Mizoram, etc.

No, you have to score more than 75% if you are from CBSE. and if you are from CBSE then you can give the exam as at the time of exam they only ask your % but you have paid the fee for then you can appear for exam but you cannot get admission in college by JEE Mains.

It depends on your JEE mains score. To get admission in this college, you need to score around 250 marks in JEE Mains.
Good luck.

You will get CSE at Heritage easily, but you have low chances of getting CSE at IEM, Kolkata.

Of course, you can. NIOS is an educational board, like CBSE, CISCE etc. It is operated & scrutinised by the Ministry of HRD, Govt. of India. Its pattern, scheme of exams are very similar of that of CBSE. Its authenticity is guaranteed by the central govt.
Now, coming to your question, not only IIT (JEE ADVANCED & MAINS), one can appear in any national-level entrance exams like NEET, CLAT & so on after passing from NIOS.

The counselling will start from 1st choice always.

Yes, you will get it in 2nd or 3rd round.
All the best.

If you want NIT. score around 300+.

Hello Akassh,
Taking a drop of one year is upto you but there are some other good private universities like BITS Pilani, VIT University, Manipal, SRM, Amrita, etc. where of is better to do engineering (B.Tech). But, it is necessary to have cleared the respective exams.
If you have cleared them and have a good rank then, there is no need to take a drop for one year.