Diploma

Check out the links below for colleges :
For Mumbai :
https://www.shiksha.com/top-engineering-colleges-in-mumbai-all-rankingpage-44-0-0-10224-0
For Pune :
https://www.shiksha.com/top-engineering-colleges-in-pune-rankingpage-44-0-0-174-0

There is no 6 year degree program. You are recommended to seek admission in 3 year Diploma in Engineering in branch of your choice. Some engineering colleges have lateral entry admission for Diploma holders in second year of B.Tech. You may seek admission in such colleges for B.Tech.

Jadavpur University should be your first choice.

Every course has it's own importance.
Select the course of your interest.
All the best

It would totally depend on your preferences. First year courses are compulsory courses and in second year you have option to pick electives and decide on which subjects you want to study. The options available to you include Human Resource, IT, Finance, Marketing, Organization Behavior, Strategy, Op

There are ample of options for students who are pursuing library sciences as a profession. Librarians, today, are not only the information providers but also make sure that the information in the library is systematically organized and updated from time to time.
While entering the field, the position

Diploma courses are generally of one year duration.

Dear Jatin,
It is always advised that complete your class 12th first before opting for any professional course. Your 12th standard marks sheet open mover avenues for you in future.

No, diploma holder can get admission through leet entry but not through JEE main.