B.Sc

Hello Mohammed,
It's very good to know your dream. It's actually very simple. Least fees are only with govt colleges. Hence you need to take admission in any college in UP, preferably in your hometown, if it is offering the stream of your choice. Normally state government conducts online admission process immediately after results of 12th are announced. You will get admission based on your marks.

IIMs doesn't publish the Cutoff. Also all IIMs have different criteria (weightage for 10th, 12th, graduation,CAT score, gender,work ex) for calling for interview.You will get more on this on IIM websites. So, it is difficult to say the minimum cut-off.
The best thing to do is to practice and score well in CAT exam.

Yes, of course, you need maths for doing B.Sc-IT and M.Sc-IT. If you have any queries, kindly revert it.

You would be eligible for most colleges as PCM are three main subjects which you need to study at 10+2 level. Please refer to the link provided below for a list of top colleges which offer courses in B.Sc. Biotechnology in India:
https://www.shiksha.com/science/colleges/biotechnology-colleges-india

Some of the best colleges offering B.Sc. in Agriculture are private colleges. Faculty of these colleges are quite experienced and know their subject. Please refer to the link provided below for a list of top private colleges which offer a course in B.Sc (agriculture):
https://www.shiksha.com/science/colleges/b-sc-agriculture-colleges-india

Please refer to the link provided below for a list of colleges offering a course in B.Sc (Medical Imaging Technology):
https://www.shiksha.com/medicine-health-sciences/paramedical/colleges/colleges-india?uaf[]=specialization&ts=15020154&rf=filters&sp[]=433

Please refer to the link provided below for details on getting admission in Chandigarh University in B.Sc. agriculture:
https://www.shiksha.com/science/course/b-sc-hons-in-agriculture-chandigarh-university-245052

After completing your B.Sc in Mathematics, you could pursue a course in M.Sc Astronomy from some of the top colleges in India. This would open up a number of avenues for you in this field. B.Sc. in Mathematics should help you as Mathematics is a major part of astronomy and space research. If needed, you could plan for a PhD in astronomy and become a teacher in this field.

Please refer to the link provided below for a list of top colleges offering courses in B.Sc. agriculture in Jaipur:
https://www.shiksha.com/science/colleges/b-sc-agriculture-colleges-jaipur