Information Technology

I would suggest you for computer engineering as it have good scope due to digitalization and you can focus on one topic, but apply to best colleges to get good placement. UEM, Kolkata will be your ideal choice for this and to know more about the college visit here:
https://www.shiksha.com/university/university-of-engineering-and-management-kolkata-47398

Both the courses have different curriculum. It depends on what your future plans are. If you want to make your career in IT sector then go for BCA otherwise B.Com will be a better option.

Tally is a go opportunity if you want to make a career in the field of accountancy. However, hardware and networking is purely different field wherein you will have to handle all the technical aspects.

Yes, polytechnic diploma is equivalent to intermediate that is 12th. You can get admission in B.Sc degree course in lateral entry mode after clearing polytechnic diploma course.
B.Sc Lateral Entry:
Duration: 2 years (Semester System)
Eligibility criteria (Qualifying Exam):
You have to clear 3 year's Diploma course after clearing 10th with minimum 50% aggregate marks in diploma course.

You can check out electronics and telecommunication engineering. It has better job opportunities in both computer and electronics industry.

IT will provide you with more technical aspects. But CS is definitely going to help in mastering low and high level programming.

It depends on your personal interest as you are the person who has to study. If you are interested in research and want to explore computer science then you should go for M.Sc as you already have science background. If you are interested in professional type of course then only you can go MCA. In keeping view of the present recession in the IT stream my sincere suggestion would be M.Sc in your case.