CBSE 12th

Every field is good. It depends on his interest for particular field. Personally, I think software engineering is the most beneficial.

Yes, you can apply after class 12th directly. BBA degree allows you to enter the field of management. This degree teaches the students with various aspects that are necessary for effective business management and essential for upcoming entrepreneurs and business managers. BBA also gives you a platform for pursuing courses like MBA.
Thank you.

No, it's not necessary that there will be a higher standard in MBA. Mostly, it depends on which college you are doing it from. You can go for M.Tech.

Do you really want to become an engineer? If your answer is yes, go for it or else go for the subject you like the most.

Hi,
If you only do BBA (or any graduation course for that matter), you are eligible to do MBA. The minimum criteria for MBA is to be a graduate. You can't directly do MBA after class 12th.
Thank you.

Yes, B.Ed will be a good choice.

Hello,
As you have studied biology in +2 as a subject, you can apply for courses like MBBS, BAMS or BHMS. The duration of these courses is 4 1/2-5 years. You can also try for courses like B.Sc Nursing or B.Pharm. Courses related to fisheries, dairy Science, or agriculture can be opted. Choose any course only when if you have strong interest/passion on that one.

Appear for IIT entrance and other entrances for engineering. Try hard to crack them and do well in them. This is the only way to get into IITs. Rest is your dedication and hard work. All the best.