B.Tech

IIT Delhi, DTU and NORTHERN INDIA ENGINEERING COLLEGE are the top civil engineering colleges in Delhi.

After B.Tech in mechanical engineering, the best streams to go for in PG are automobile, mechanical, robotics or Production Engineering.

I dont think all NIT's have this provision but yes there is a provision of branch change after 1st year though the requisites for the same may differ
Like in NIT Kurukshetra you have this provision. You can apply for branch change provided you dont have any backlogs in the first year and leaving you

There is not a standard best or worst course in engineering. Choice of branch really depends upon your interests. If you are interested in computers and coding, go for CSE. If you are interested in machine design and automotive, go for mechanical or automotive. If you are interested in electric circ

You can get admission through management quota but management quota admission and fee cost is not advertised openly by any of the colleges/universities across India as being a paid seat it totally depends on the discretion of the college authorities.

Check out the link below and click on know college cut-off:
https://www.shiksha.com/upsee-college-predictor

Galgotias engineering college is a good option in terms of faculty and placements but to know the exact scenario, get in touch with the current students through social media or in person.
* Don't take admission in galgotias university because many people confuse it with galgotia engineering college

MCA after B.Tech will make no sense because as per industry standards B.Tech and MCA students are placed at the same level during placements even though the MCA being the PG degree.
I would suggest you to either go for MBA or M.Tech as per your interest area