Diploma

No, you can't pursue it after diploma from an electronic background, however, you may have the chances for some colleges.

Well, the thing that matters is your interest. Whichever field you're interested in, go for that.

You can apply after 12th and the fees depends on the college which you will prefer.

Yes, if you want to do a job then you can but you can only pursue BA or distance mode of education type course. You can't pursue any professional courses because after the supreme court order none of any pro courses can't be done via distance mode of education.

Yes, you can join diploma after 3 years but you have to give a proper reason in written why you had opted gap and your reason should be genuine.

Yes, you are eligible but you have to crack the entrance exam of JEE Mains and JEE Advanced and your 10+2 marks should 90+.