BBA

Yes, you are eligible. But please check your age according to college eligibility criteria.

You can change your course but you can't get admission in 2nd year, you have to take admission in 1st year with new course and you can't get admission in between the year you have to wait for next year.

Admission is based on the marks obtained in class 12th.

No, it doesn't offer integrated courses. But, you can pursue both the courses in VIT.

BBA entrance exam mainly based on basic concept till 10th class aptitude, general knowledge, reasoning, English. This is the syllabus subject for BBA exam so do practice on basic concept and refer RS aggarwal book for aptitude and reasoning for general knowledge refer newspaper and monthly current a

English Language, Comprehension Skills, Verbal Reasoning, General Knowledge, Current Affairs, Quantitative Aptitude, Numerical Ability, Fundamental Mathematics Operations, Critical/Analytical/Logical Reasoning, Data Analysis and Interpretation.
This is the whole syllabus for BBA. Kindly check it.

You can download from here https://www.shiksha.com/science/cucet-exam-question-papers.

No, they are different as the courses itself are very different, B.Com is about commerce and BBA is about management.

Doon University does not offer BBA only. It offers an integrated course of BBA + MBA and the total fees is Rs 3,70,000 with an yearly fees of 74,000.