B.Tech

Both are good but DTU is old and reputed so I will suggest you going with DTU. The placement record of both the universities is almost same.

Though most of the UK universities accept the Indian graduation system of three years for entry into most of the postgraduate courses with a completion of 15 years of education, some courses and universities may require a qualification equivalent to British Bachelor (Honors) Degree, which requires 1

No, if you are going through civil engineering then there is no chance go jump from civil to aerospace. For further studies, you may take degree of specializations in any one field of civil engineering.

That's good if you are not selected in campus by company then don't need to worry you are left with many option you may go for M.tech or you may prepare for gate exam so that after clearing gate exam more option came.
For IAS, there is only one Brand name that is Chanakya IAS Academy.

Please check the college details here:
https://www.shiksha.com/b-tech/resources/mhcet-college-predictor

Please follow the below-mentioned link for complete details about college:
https://www.shiksha.com/b-tech/resources/mhcet-college-predictor

Yes, you can get a seat in Chandigarh University. .
Not only that you can also get a scholarship of 50% once the admissions are done.