B.Sc

In web designing there are ample opportunities available. The field of web designing is growing at a very fast pace. You need to do a thorough research in order to pursue this course. You can opt this course in Ahmedabad as it has good web designing institutes.

I think BCA would be a better option but to get jobs in some of the reputed IT Companies, only BCA is not enough. You need to go for a Post Graduation degree such as MCA, M.Sc IT, M.Sc CS, MBA IT, etc.

The criteria is that you must have completed your class 12th with 60% aggregate and 75% to 85% in your honors subject (Zoology, botany and chemistry). Zoology honors need 60% marks in chemistry.

Yes, you are eligible to get admission in B.Sc after completing class 12th.

You need to keep in mind that animation and visual effects is a very dynamic field. It requires constant upgrades to the curriculum. I doubt such flexibility is available in any of the degree programs. Moreover, this is a skill oriented field and certificate seldom matters.
Before you chose a program, you should try to understand the work culture of this industry. It is very different from all the other segments. Take a session with experienced career advisors of this field. They will be able to help you understand. You should compare the course content, check the placement record and faculty experience too.
All the best.