Polytechnic

Yes, you can definitely think of doing B.Tech after the completion of your Diploma.

If you have done polytechnic then you can get admission in direct second year otherwise, you have to start from the first year itself.

Yes, you can do BBA in airport management after doing Diploma in ECE because for BBA what is needed is 12th or any equivalent without any specific subject. The course of airport management has scope in aviation and flying. However, before that you should be a graduate in a particular stream from a recognised college or certified institute. Other BBA specializations like oil and gas management, and financial marketing also have good scope.

The semester wise detailed fee structure for courses of University Polytechnic, 2018 batch, can be viewed here:
https://www.bitmesra.ac.in/Show_Content_Section?cid=12&pid=351.

Yes, it will be right, no problem. However, it is best when you do it after 10th.

Yes, it is helpful. If a student wants to make a career in engineering field, then starting from the very basics gives you an advantage for higher studies. The three-year Diploma makes them eligible for direct admission into second year of any engineering degree course.

You may check this link :
https://www.shiksha.com/b-tech/course/b-e-lateral-entry-Jabalpur-engineering-college-232518