Diploma

There is no specific marked valued qualification. However, if you are interested in money and technical side, you may opt for SAP MM consultant. THe certification from authorised centre may cost you around 4 Lacs.
You may also look for MBA in operations or MBA in supply chain in part time mode.

Yes, I don't think there should be any problem for students with a one year gap after completing your diploma. Nowadays, it is very common for students to drop a year to gain admission to a college of their choice.

You are eligible for BCA even after Diploma in E&C, hence you can pursue the same.

I would recommend you to join 1-year Diploma course in hardware instead of 3 years Diploma because hardware is not such a big course, details mentioned below:
Diploma in Computer Hardware and Networking is a short term course that educates the participants with hardware parts of the computer and net

AMIE is having a good scope. The important thing to be noted here is that you should look for a reputed institute for this course.

It is interesting to hear that you need to do Diploma after B.Tech. It is better to take MS from Canada instead of Diploma.

It is better to go for a job related to your field. B Tech is one of the options which you can use. A large number of automation electronics courses are available. Try to surf the internet!