Kolkata

You should score above 70% overall in HSC and 70 narks in the subject in which you want to take Honours.

Below are the colleges in Kolkata to pursue Diploma in interior designing:
https://design.shiksha.com/diploma-interior-design-courses-in-kolkata-categorypage-13-70-412-0-0-130-127-2-0-none-1-0

Yes, but you will be provided opportunities to get internship outside Kolkata also.

Glamour Institute of Fashion and Interiors is good Institute for doing Interior Designing Course. It is good Institute in every terms like training education and placements.

We provide a wide list of coaching institutes in Kolkata.
https://www.google.co.in/url?sa=t&source=web&rct=j&url=https://www.myprivatetutor.com/institutes/kolkata&ved=0ahUKEwjuk5SchbbUAhVIM48KHQ9ZAX8QFghsMAM&usg=AFQjCNHZd_zKCyLg8QjC8Qx6vKj-wIYTJQ&sig2=EyOOE-BIKH2jD0KgMlvhog

Hello Aparna,
Yeah, for sure, you can take admission into IEM, Kolkata via your JEE Mains rank but for this you need a rank under 50000 to get any good branch, however, considering your rank your chances are nil.

Hello Rakesh,
Heritage and Haldia are not very much known for lucrative packages, so if you are considering mechanical branch and looking forward for heritage and Haldia then you might be on wrong path, however if you want to be placed in top notch companies with high packages then look forward for IIT's/NIT's and BITS, Pilani.