B.Com

Yes, you can go for B.Com after Science in 12th. Eligibility for B.Com in most of the top universities is Pass with 50% aggregate marks in 10+2. (it may vary with the university you choose). In some of the colleges, one has to face the disadvantage of marks in the best of 4 because admission for B.Com takes place through a merit system. The standard disadvantage allowed is 2.5 %, but it depends on colleges as some colleges have a disadvantage of 3% or even 5% but not beyond that.

You can take admission in any college. You will have to prepare for CA separately anyway.

I hope this link will help you :
https://www.shiksha.com/accounting-commerce/colleges/b-com-colleges-Chandigarh.

Please refer to the link below for B.Com courses:
https://www.shiksha.com/accounting-commerce/colleges/b-com-colleges-india?rf=searchWidget&landing=ctp.

The total fee of the course is Rs. 1,35,200 for three years.

No, the college does not have a sports quota.
You can refer their prospectus for details: https://www.jbascollege.edu.in/media/Shift-I UG Prospectus 2018.pdf

It doesn't make any difference as CA is a professional certification. Especially when it is B.Com with any specialisation, it becomes an added advantage. Therefore, I personally think you should go ahead with it.
I hope this helps. All the best and god bless you.

Yes you can do B.Com in accounts.