B.Com

You can not shift to National Law Universities because as of now, there is no lateral entry admission process in NLU. You may appear for CLAT to seek admission in NLU for 5 years integrated law program.

Go as per your interest.
If you are good in account and finance related things, then B.Com is good and If you are interested in business administration things, then you should go for BBA. If you want to make your career in management, then you can go for MBA provided you do MBA from a good college.

If I talk about the best colleges in India, undoubtedly it is SRCC of University of Delhi. To make it to there, you probably need 99% in 12th standard but once you are in then nothing else can stop you from achieving good heights except yourself.

Institute of Cost Accountants of India (ICAI) [previously known as the Institute of Cost & Works Accountants of India (ICWAI)] promotes, regulates, and develops the profession of cost and management accountancy in India.
There are 3 levels:
Foundation, Intermediate and Final examinations and three years of practical training.
Exams are held twice a year - June and December.

Kindly visit the links given below to get the details:
https://www.shiksha.com/B-Com-Hons-course-in-Noida-Au-Amity-University-Noida-course-information-listingcourse-206820
https://www.shiksha.com/Au-Amity-University-Noida-Noida-institute-college-listingoverviewtab-41334
Yes, it is a good option for B.Com (honors) as you can go with it.

Christ University
Jain University
Acharya Institutes
St Josephs
Kristu Jayanti
Alliance University

It's difficult to get DU colleges for B.Com/B.Com (hons.) without maths in 10+2. You must have maths in 10+2. There is no cut-off marks to be achieved in maths, just having maths as a subject is fine.