Company Secretary

If you want to do MBA after BBA then CS is not necessary. You can do MBA after BBA. But if you have interest in CS then go for it, gain some work experience (1-2 year)n and then go for it, so that it would be better for your admission and placement in an MBA college.
Provided you do MBA from a good college so that would better for your career growth.
Otherwise, you can also do BBA only gain work experience and then go for MBA.
It depends on you.
Best of luck.

The Company Secretary (CS) Course conducted by The Institute of Company Secretaries of India (ICSI) has three sections: (a) Foundation (b) Executive (c) Professional.
The minimum eligibility required for the foundation course for Company Secretary is 10+2 or an equivalent examination. Candidates who have enrolled for the 10+2 examination can apply with the proof of passing the examination within 6 months. You are eligible to apply for Foundation course of Company Secretary.

It is a three level course. Foundation, executive, professional. A student has to go through 15 months of practical training which he may opt after passing the executive programme.

Post graduate courses in securities management, quantitative finance, risk and treasury management and capital markets are all available in National Institute of Securities Markets (NISM).
Similar courses are also dispensed by CCGRT (Mumbai). On the same note, certifications and licenses are also given by BSE and NSE relating to compliance's.
You can always go for another undergrad degree or a Masters degree. For instance, student who have done B. Com enroll for M. Com or LLB, or the ones who have completed LLB enroll for LLM.

No, if you are pretty confident about your preparation but coaching will definitely help you.

B.Com (Honors) from a good college with good teaching faculty is the best degree course for CA aspirants as it will help you in your CA preparations.

Yes, you can pursue, provided you are very hardworking and have a lot of patience.
All the best.

Yes, CS is a very good option for you but in CS you are going to study company law so think before choosing a course among CS, CA and CMA.