Computer Science

Yes, you can take admission in that college.

Yes, As your category is SC, so, it may be some hope to get admission in lower order NITs.

Yes, you may not count maths in best four subjects.

The decision would depend on your long-term career goals. In case you intend to pursue a career on the technical /programming side then MCA will be more suitable. In case, you intend to explore a career in general management then an MBA would be more effective.

Dear Ashish,
The fee structure for B.Sc in computer science is Rs 35,000/-PA.

Dear British,
I doubt if this is possible as the min. Eligibility is 70%, check the link below
https://www.shiksha.com/science/course/b-sc-in-computer-science-vit-university-Vellore-119915
Better would be to try for admission in good universities like Lovely Professional University, Christ University, Periyar university, etc. Where you would be able to meet the eligibility criteria. All these universities have wonderful infrastructure and world-class facilities. LPU offers good placements and handsome scholarships too.
Good luck.

Yes, why not. You've studied all those subjects. So, you can sure chose them as mainstream.

Yes, after completion of BCA, you can join M.Sc Computer. But you need to find the cutoff for this college because your BCA marks are low.