IIT

It depends upon the branches.

What is your category?

You can try your luck in DTU counselling. IIITs and NITs seem to be tough with this rank but anything is possible. You just need to have patience and wait for all the counselling till spot round. GFTIs are not as much better option as the above two are, so keep that as a back up plan. All the best.

You are eligible for sure but you have to clear JEE Mains and then, you have to clear JEE advanced to get a seat in 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.

Sorry, you cannot apply for IIT or any engineering competitive exams if you had completed your 12th from any other stream rather than science which must include PCM because it's one of the eligibility criterias.