Fashion Design

NIFT is one of the best college.

You don't need to go for another UG program in fashion, if you are already a graduate. You can just go for PG program, be it degree or Diploma from any reputed fashion institution.

Both have equal scope.

The course related to fabric and garment manufacturing is basically fashion designing, like for Bachelors it is B.Des. in fashion designing and for Masters it is M.Des. in fashion designing.
In this, you'll be taught about the fabric and garment manufacturing in detail. If you just want to go with the fabrics then you can do something with textile designing and that is also a good option with a lot of scope.

Yes, you can pursue Masters in fashion designing. To get into a good college such as NIFT or NID, you need to appear for their entrance exams, so start preparing for the same.

I would suggest you to go for a degree course, as that has more value and will help you get better job prospects.

The main objective of internship is to get the practical knowledge of the industry. It is always better to go for as many internship as possible because it will give you the industrial experience, which will definitely help you in your future.

No, it is not necessary to do fashion design.
Below mentioned is the minimum criteria to enroll in any post graduate course:
1. Minimum 50% marks at higher and senior secondary level (Class 10th and 12th).
2. Graduation with minimum 50% marks from a recognized university.