Science

Yes, you can get a seat in Andhra University.

Andhra University announces management quota seats, please check this link:
audoa.in

BBA is a Bachelor of Business Administration and if you want to opt for this you should have some knowledge or interest in business management. Whereas, in B.Tech you have the opportunity to create something new and interesting. B.Tech requires analytical skills and a good problem solver along with

Yes it is. There are various career options like Agricultural Engineer. Many people don't think of farming as being sophisticated. .
Animal Scientist. .
Biochemist and Biophysicist. .
Biomedical Engineer. .
Epidemiologist. .
Food Scientist and Technologist. .
Microbiologist. .
Soil and Plant Scientist.

Yes, you are eligible. A general Maths can opt general Science branch easily by just fulfilling the educational qualification of the course.

Though you have got good rank in ST category, you will get admissions. You may have to compromise with the branch or courses. Or, you can go till the end of counseling for getting your selected course, where you can get and you shall get. Please specify which course you want to pursue in BHU.