BCA

You are not eligible to seek admission in BCA unless you clear 12th class.

For BCA it is not at all necessary to do 3rd year in any foreign college it will be in Christ College only, however they do offer you a program in which 3rd year studies are done in any of the affiliated colleges abroad.

Visit the link given below:
https://www.shiksha.com/it-software/colleges/bca-colleges-pune

B.Tech CSE is the first priority. If you are getting IITs, NITs, VIT, BITS-Pilani or other top institutes then B.Tech CSE is the best otherwise you can go for BCA.

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.

Hello Sandeep,
Either of these degrees would do to get admission into any B-school in India. There is no compulsion for an aspirant to pursue a particular degree or set of it. Choose the one which suits your interests and career goals more.

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.