Diploma

Yes, it's a good option but it will be better if you opt for Bachelor's for a good job.

For good placements, you should crack JEE Main and JEE Advanced for better government College. And None of private College except bits Pilani etc. And for these private colleges you'll also have to beat entrance exam.

Yes, you can get but better you should opt some post Diploma courses from Indian maritime University.

Yes, you can pursue diploma in fire and industrial safety.

After completing the course, graduates may get hired at major International or Domestic Airports. Average starting salary is usually between 3-6 Lakh Rupees per year. Job roles available are-
Airport Manager
Administrator
Staff Manager
Safety Officer

No. There is nothing which can give you online Bachelor's in engineering. But, you can get your Bachelor's through AMIE via distance learning it's a B.Tech equivalent but some companies and colleges not accept Amie holder.

There is no college which can give online Bachelor's in engineering. You'll have to attend the classes and your attendance should be 70% to appear in the exam. And
yes, you can get lateral entry if you have Diploma.

Fee will be around 35K for diploma in interior designing.

It totally depends on the discretion of the college. I would recommend for all such specific information, kindly get in touch with the college officials.

Hello Rajit Kumar,
Yes, it's very nice of you to think of doing engineering via lateral mode after completion of your Diploma in Engineering in IT. After doing the graduation your chances of getting placed increase tremendously. In the state of Uttar Pradesh for entry via lateral mode in engineering