MCA

Yes, you can get good college, but you need to score at least 60% in class 12th in order to be eligible for good universities. Yes, you need to do BCA+MCA, and it will be worthwhile.

It is a good institute for MCA or other courses as well, but the major problem is with scoring marks in your semester, as their marking is difficult.

Yes, you can pursue MCA course without having Maths in your graduation. Good luck.

No, you have to study first year too for MCA.
Good luck

Yes, you can apply for government jobs with your graduation and post-graduation.
Good luck.

Some of the colleges you may look for:
University of Mumbai-Fort, Mumbai
VJTI Mumbai - Veermata Jijabai Technological Institute- Matunga East, Mumbai
Amity University, Mumbai- Panel, Mumbai
NMITD - Navinchandra Mehta Institute of Technology and Development-Prabhadevi, Mumbai
The L F College of Engineering & Management-Andheri East, Mumbai
ASM's Institute of Management and Computer Studies (IMCOST) - Thane West, Thane
University of Mumbai-Fort, Mumbai
VJTI Mumbai - Veermata Jijabai Technological Institute- Matunga East, Mumbai.

Yes, if you have completed your graduation in B.Sc, you can surely apply for MCA.

As you have completed B.Sc in Mathematics, looking the future demand and scope of the course and career better opt for AI courses.

You can visit this link
https://www.shiksha.com/resources/college-comparison.

Yes, IITM is a decent college and have all the facilities like modern labs, library, Wi-Fi campus, good infrastructure as well as good faculty team. Good luck.