Institute of Management, Nirma University

As you say that it only accepts the CAT scores, I don't think there will be any chance for admission there still you can contact the admission cell of the college and also visit the college website for further assistance.

NIRMA university is the best option among others.

You should consider wearing formals. For PI, be yourself and present yourself in a way which shows your eagerness to get into this college. Don't fake or guess the questions, you don't know, simply tell that you are not aware of it.
Another point is to prepare two three topics of your interest upon which you can talk. That's it from my side.
All the best.

Both the courses have equal importance but in my perspective in today's scenario PGDM is good but it should be equivalent to MBA by AIU (Association of indian university)

CAT is the only way to get in here.

There is no eligibility. It all depends on your caliber and interview skills along with more than 60% across.

Batch has not starrted but admission process has started already.

No, you can not get any admission in such manner unless and until you belong to NRI Quota.

Yes, officially you have to apply to get a call for GD/PI process.

Then, you have no chance to get in. Try some other institutes.