IIT

If you are determined to get into CSE in any IIT then you should take a drop.
As your rank is also not good go get admission into any IITs, so you must have to do something either taking a drop or taking admission into some of the private colleges.

As per recent news, there were no announcement regarding one course for engineering.
So, the chances for MHCET to be happen in 2019 is more.
Wait for the further announcements.

Yes of course, you can join preparatory course in IIT if you qualified under preparatory course in JEE Advanced in your very first attempt.
Generally, the cut-off for preparatory course is less than general cut-off.
Thanks.

You can check the cutoffs but your chances are less.

Chances of IIT Nagpur is over, as IIT is given to those who qualify JEE advanced.
JEE Mains qualified students are eligible for admission into NITs and GFITs only.
Now chances for VIT-Pune is in your range. Do try for VIT-Pune.
Best of luck.

For your category, JEE Mains rank for CSE branch is under 20k in NITs and DTU but in IITs, you should score under 2000 rank for CSE.

Dear,
As per the market demand and jobs, you would get more opportunities in civil engineering. Petroleum engineering is a good field and has a good growth but job market comparison to other branches is less specially in India.
All the best.

There are many colleges which are good as IITs and NITs such as BITS, VIT, SRM, MS Ramiah, KIIT, Manipal University and Manav Rachana University.
But if you want to take admission this year then you can try in Sharda University, Amity university, LPU, Chitkara University, DIT University, Graphics Era

The exam for HBTU from 2017 is going to be JEE Mains itself. So, now the exam is JEE Mains and previously it used to be UPSEE. You can do your regular JEE preparations for it!

I would suggest you to continue with B.Tech in engineering design from IIT-Madras.