Career

You have to study psychology in graduation. For that, you need to complete your class 12th in science or arts stream. Opt for psychology in graduation. There are few institutes in India which offer courses for certifying you as a psychologist. You will have to do the courses from there.

A search on the net will lead you to many coaching institutes for IAS preparation. Getting a comparative study is also easy now-a-days. I want to tell you about some latest options for coaching. Many people are opting for online coaching classes which are affordable and good. They are conducted by experts so you need not worry about their effectiveness.
For example a visit to a site WizIQ.com will show that there are fifteen different types of courses (https://www.wiziq.com/courses/search.aspx?qry=IAS) available. You will get an idea about their popularity from the number of students taking the course. No harm in exploring.

Yes, it is a good career option if you are really passionate about it. It involves knowledge of History, Anthropology and such similar subjects. It is meant for a person who has the patience and knowledge for doing research. If you are good, then you may be employed in museums or government departments.

You need to complete your class XII exam successfully, and then appear for the entrance examination conducted by the National Defence Academy. It is very competitive because of large number of examinees, and one has to prepare rigorously. For detailed information, check out the link mentioned below:
http://nda.testbag.com/exam-analysis.php?tp=4

Yes, you can switch your career to computers field from commerce stream. There are a lot of PG courses available after class 12th with commerce stream that you can pursue. Some of the courses comprise:
MCA
PGDCA

Since you have completed your MCA, I would suggest you to go with a Ph.D or ME in computer science.

Doing MBA in Canada will give you a very bright future in India. It will give you the first hand knowledge about management and how to tackle and control a company. It will incorporate certain qualities in you which are required to become managers. You can pursue MBA after any Bachelors degree. It would make you work in the field of:
Accounting
Sales
Human resource
Finance
Stocks
Economy

In public sector, majority of bank managers are through route of PO examination. Majority of private sector banks managers are a direct recruit MBAs.

The admission for the above mentioned courses will be done on the basis of score obtained in MH-CET only & not on the basis of NEET.