B.Sc

Some of the best options include:
National Institute of Rehabilitation Training and Research, Cuttack
S.R.M. Institute of Medical Science and Research, Chennai
College of Allied Health Sciences, Manipal Academy of Higher Education, Manipal

After 12th commerce, you will not be able to pursue B.Sc IT because for B.Sc IT one should have passed in science stream. If you are interested in computers then you can pursue BCA and then MCA. This has more scope as compared to B.Sc IT.

No, presently, School of Open Learning provides correspondence courses in commerce subject only.

You are eligible to do MBA after the completion of B.Sc. You are in a position to crack MBA entrance examinations easily because of your superior numerical and data interpretation ability as you are a mathematics graduate. If you can improve your verbal ability, you can crack CAT and have an excellent management career in any management function of your choice.

Indian Institute of Science, Bangalore is the best one.

Yes, you can opt biogenetics in agriculture.

You can pursue a PG course. The matter doesn't end there. Do either a Ph.D. or appear for NET. If you want immediate results, go for B.Ed.