Colleges in Delhi

Eligibility criteria for seeking admission in MStat at DU is Bachelor's degree in any subject and candidate should have studied at least 3 courses each of one year duration or 6 courses each of one semester duration in Statistics under 10+2+3 scheme of examination OR
Bachelor's degree in Mathematics (Hons.) or Computer Science (Hons.) with at least one paper in Statistics under 10+2+3 scheme of examination of the University of Delhi or any other examination recognized as equivalent thereto 50% marks in aggregate and 60% marks in a paper of statistics .
You are eligible to seek admission in MStat at DU.

You should appear for JEE Mains Advanced first.

I will send you the link, you can check your college according to your rank:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

India's oldest B-School IISWB&M, obviously, you can expect better job stability and in hand salary and the cost is also lower than IMI, so RoI is high.

That is a very tricky question. Most top colleges cut offs are in mid-90%. So, you do not have the chance to get through in top colleges. But, for some courses DU cutoff's are less (not sure which subjects you are looking for).
Otherwise, there are many more options - JMI University is best, IPU is reasonably good.
Besides these, you can opt for private universities in Delhi NCR.