CA

Yes, you can pursue CA after humanities but you have to focus on basics. First, you have to take CPT Entrance Exam which is held in June and December every year.
Take coaching of it and also take coaching for Basic of accounts so that it's better for your long run in CA or you can also go for CS
Otherwise, you can also pursue B.Com or BA but and pursue MBA later from a good reputed college.

If your background is maths, then yes you can do CA.

Yes, you are eligible for CA.

You are eligible to pursue MCA, M.Sc IT/CS and MBA. If you want technical career then you may opt for MCA or M.Sc else MBA. Based on your background and shared personal details MBA will be a better option for you.

Law is quite a crowded career place and is full of independent consultants. CS is not a field to be in independent consulting field. Best option for you is to do CA. You can work with a CA firm and after few years experience start you own Consulting Firm.

CA+CS is a professional career & personally, I would rate it higher than MBA+CS. Since, you have mentioned that you are interested in Law as well then a CA qualification would be of a lot of help to you for specialising in legal matters related to financial domain.
Even if you are not able to clear CA, a CS & LLB will also give you a professional career as a company secretary/consultant in a law/advisory firms.