Is CS a good option for me if I am interested in theory based studies? Is it good to pursue MBA after CS?

First of all, clear your myth that CS isn't a theory based course. Since it consists so much of law hence it is not theory based. It is all about practical and interesting to study as well. No, MBA won't be a better option alongside CS. The better option is LLB related to the field.

Go for CS as after the implementation of the Companies Act, 2013, CS are in high demand. Company secretary is very lucrative and with the implementation of companies act, 2013 the scope has widened for a company secretary as a professional. If you want to study easily, CS. (Easier of the two), More