M.Tech

You need to have a minimum of 60% in your 10th, 12th and graduation degree to pursue this course from a good college.
You can do this course from one of these colleges:
1. Rajiv Gandhi Proudyogiki Vishwavidyalaya, Indore (madhya pradesh)
2. UP Technical University (Instt of engineering and Tech) Lucknow
3. Visveswariah Technological University, AIT, Chikmagalu
4. UPES, Dehradun - This College provides further specialisation in offshore structures, check their website for further information.
5. Thapar Instt of engineering and Technology, Patiala
6. IIT, Delhi, Kanpur, Kharagpur and Madras
7. Jamia Milia Islamia, New Delhi

It is always better to go for post-graduation than doing Diploma or certificate course. If you have completed your graduation, then you should definitely go for M.Tech, you can do the certificate simultaneously for more knowledge.
A post-graduation degree always upraises your level and position and pay scale. For doing M.Tech, you can apply to various colleges:
1) IIT's.
2) DTU – Delhi.
3) Thappar University – Patiala.
4) UPES – Dehradun.
5) NIT's.

M.Tech is for design and teaching careers. For construction careers, B.Tech is sufficient for any company.

You can visit the below mentioned link for detailed information: https://www.shiksha.com/university/noida-international-university-greater-noida-53337/courses/me-mtech-bc

You can check the below mentioned link:
https://www.shiksha.com/college/dy-patil-school-of-engineering-dypsoe-lohegaon-pune-40764

Yes, you can take admission in BHU, Varanasi for this course.

It depends on your own interest. You can go for M.Tech in production and design.

You can go for MBA and you will find better options further.

Hi
You can pursue B.Tech immediately after your completing your 12th and giving the common entrance test for admissions. As Mr. Sunil Soni said, BE and B.Tech is the same degree. It depends on the college you select. You can apply to the various colleges like:
1. BITS, Pilani
2. IIT's
3. UPES, Dehradun
4. Vellore institute of technology, Tamil Nadu