M.Tech

It has a good scope. Plus, it take one year off your studies but, the 5 year programme is pretty hard with all the course and studies.

Top Institutes offering B.Tech in nanotechnology are:
SRM Engineering College
Amity University, Noida
University of Technology, Jaipur
Aurora Group of Institutions
BITS, Hyderabad

Currently, NIT-Shillong is providing part time M.Tech, check out the details below :
http://2018nitm.nitmeghalaya.in/p/mtech-part-time-1.

No, that is not possible. BE / B.Tech( Mechanical Engineering, Civil Engineering, Marine Engineering, Naval Architecture) is a Mandatory Course.
Check out the details below:
https://www.shiksha.com/engineering/course/m-tech-in-naval-architecture-and-ocean-engineering-indian-maritime-university-chennai-visakhapatnam-campus-276778.

Hai,
Placements for M.Tech are vast in both public and private sector. Nowadays, the trend of job opportunities are more in communication systems or in Data Analytics. Job opportunities in Private sector are huge for Data Scientist or Data Analyst positions. For this, you can go ahead with M.Tech in Computer Science and Engineering.

All the leading IITs and NITs are providing integrated B.Tech plus M.Tech-
IIT Kharagpur
IIT Bombay
IIT Madras
NIT Rourkela
NIT Hamirpur
Other institutes are:
JIIT Noida
VIT university.

Of course. My opinion is- Don't go for M.Tech. You already have MCA that is Masters degree. Search for a good job n do hard work in it to get early progress. All the best. Please like and follow bro.

Hi Deep, IIT Roorkee is one of the good IITs for M.Tech in soil & water conservation. Thanks.

No. You need to have a B.Tech degree.