Mechanical Engineering

Before going for your visa interview, you have to take the decision regarding your study program either MS or PGDM. You can pursue both simultaneously.
All the best.

Yes, you can definitely choose M.Des. after doing B.Tech in mechanical engineering. You can either go for industrial or transportation design, both are equally good in terms of placement and are relevant according to your degree.
There are only two colleges that have M.Des. in transport design:
1. MITID, Pune
2. UPES, Dehradun
Top colleges for M.Des. in industrial design are:
1. Lady Sri Ram College, DU Delhi
2. NIT, Bhubaneshwar
3. NIFT's
4. IIT, Roorkie
5. UPES, Dehradun

Below mentioned is the list of universities for mechanical engineering in Germany:
https://www.daad.de/deutschland/studienangebote/international-programs/en/?p=l&q=mechanical°ree[]=2&fos=0&fee[]=0&sortBy=1&page=1&display=list es.html

After completing your Diploma in mechanical engineering, you can opt for CADD as it is the best course. Either you can opt for:
1. Marine.
2. Biomechanics.
3. Piping and
4. Aeronautical engineering.

Follow the link and filter colleges according to location :
https://www.shiksha.com/b-tech/ranking/top-automobile-engineering-colleges-in-india/51-2-0-0-0

Your chances of getting admission are not very bright but it is worth a try.
All the best.

Management Courses related to mechanical engineering are Total Quality Management (Kaizen, 5S, Six Sigma), Operations Management, Logistics Management. These are some of the management courses in which after pursuing Mechanical Engineering you may get benefit.

If you have completed your Diploma then you are eligible to get 2nd year lateral entry admission in B.Tech in any college after giving the entrance exam. You can study NCERT books and the basics of the syllabus you have studied in your Diploma for its preparation.