Its good to see that you are not just exploring the career options but also exploring yourself and your interests.
While discussing your queries we will go one-by-one:
1) You say that you are pursuing your 12th commerce.A career in psychology would require you to shift to arts.Psychology these days is a field which is in demand,hence the competition in the field has grown and so have the opportunities. The selection criteria has also become stringent. That means the colleges in order to take students for BA psychology majors,
specifically select students who have had psychology till 12th or at least have taken arts till 12th. This varies from college to college. SO you need to start off by looking at your options right away.
2)The B.A. in Psychology focuses more on the social aspects of the study of human behavior and psychological function, and the B.Sc. degree focuses mostly on the biological and biochemical basis of behavior and mental function. Although these focus areas overlap, the background and experiences necessary to pursue one focus area or the other are quite different. The B.S. degree has a heavy biological and physical sciences emphasis.
So if your interests are in areas such as: Counseling Psychology, Social Work, Industrial and Organizational Psychology, Social Psychology, and Developmental Psychology, then you would benefit more from taking the B.A. in Psychology.
If your interests are in areas such as: Biopsychology, Psychopharmacology, Neuroscience, Psychiatry, Neuropsychology, Sports Psychology, Physical Therapy, Pharmacy, Genetic Counseling, Public Health, Medicine, Dentistry, and Veterinary Medicine, then consider opting for the B.S. program.
3) A BA would give you a foundation and will expose to various subjects like abnormal psychology,counseling psychology,social psychology,research methodology and statistics etc. While a MA would lead you to a specialization like counseling, clinical, industrial, personnel etc. Just completing a BA would not equip you enough to make a full-fledged career in the subject.
4) While our site states the remuneration, its a starting salary that one can expect. And moreover, if you look at working with a corporate certainly the pay would differ drastically.
5) In order to make a successful career out of any stream one needs to be passionate, and once that happens everything else falls in place. SO certainly you can be successful!!
6) You can pursue a career in India or abroad, its up to you to decide. But universities abroad offer a lot many options hence that would be an ideal choice.
Its advisable that once you have more or less decided on psychology, visit our study abroad cell. The experts there would be able to guide you and help you select universities and help you with their procedures.
Hope this helps.
kindly revert for further queries.