Economics

Yes, you can apply for CSIR Mathematics/ NET in Mathematics after completing MBA in Finance.

You can opt for private colleges, as many colleges don't take admission below 40%, but don't get sad try to apply to colleges.

When you take admission in a university, the board through which you cleared your 10+2 does not matter. The difference between the two boards is in the difficulty level. If you choose CBSE, the difficulty level is much lesser than that of ICSE. So choose the board on the basis of the pressure you are willing to take.

Kindly visit this link for information about placements at Mithibai for M.A. in Economics
https://www.shiksha.com/college/mithibai-college-of-arts-chauhan-institute-of-science-amrutben-jivanlal-college-of-commerce-and-economics-vile-parle-west-Mumbai-48353/placement#:~:text=Placements:

After completing an M.A. In Economics, you can either continue to pursue higher education like M.Phil/Ph.D. , or you can make a direct entry into the job. Hope this helps. Thank you.

Details about the college and the course is given in the link below:-
https://www.shiksha.com/university/amrita-vishwa-vidyapeetham-Coimbatore-52263.

You need to have a relevant B.A. Degree from du or from other recognised university with 60% in aggregate.

Yes you have a fair chance of getting into NMIMS Mumbai campus but do check out their cutoff.