Diploma

Hello,
Though it's purely your choice to pursue a course as per your own interest, I would suggest you to opt for Aeronautical Engineering. Following are the reasons:
1. It's better to stick to the same field wherein you have already learnt the basics. Bio-Medical Engineering is a specialization in a completely different domain, while, Aeronautical Engineering is related to Mechanical Engineering.
2. Being in a similar field, it will open up diverse job opportunities for you as you can opt for jobs in the Mechanical sector as well as Aeronautical sector.
I hope this answers your question. If you have any further questions, kindly revert.

No, if you are doing diploma in mechanical engineering you cannot apply for IIT or NIT because it has stopped taking any lateral entry admission and if you have done your 12th then you can surely apply for the JEE mains advanced.

Yes, you can apply for engineering abroad after doing diploma in mechanical engineering from India and also you can get lateral entry in the second year of B.Tech.

Yes, you can take admission in aeronautical engineering after doing Diploma in mechanical engineering. You can opt for Lovely Professional University that offers the same.

You can choose Diploma for computer engineering because it has very good placement in future.

The main reason why postgraduate courses are named as PGDM is because when an Institute is an autonomous body (not affiliated to any university) and conducts management courses, then such Institutes cannot offer MBA degree. Even IIMs, XLRI's doesn't offer MBA degrees; they only give PGP Diploma. I hope this would suffice.

Yes, Diploma holders can take admission into 2nd year of B.Tech through lateral entry scheme.
Several institutes conducts admission through CET, or different states conducts a different type of entrances for it (example-west Bengal conducts its own entrance for it).
However, candidates can also appear for AIEEE and IIT-JEE.

Hi Shri,
The cutoff varies every year according to the number of students applying for examination and number of seats available. It would be advisable that you get in touch with college authorities/official page directly for accurate cutoff.