CBSE 12th

What is your locality city? There are lots of metro cities, where you can join the colleges for B.Com (Hons) reply with your locality.

CBSE syllabus has very good reputation all over India. In case of graduation also, your plus two marks will be considered. If you can score better in HSE, then it is good to shift.

You can go for your state government engineering colleges, as you have scored less marks. Or, you can also go for private colleges.

For admission in Jadavpur University, architecture department WBJEE GMR(General Merit Rank ) is necessary along with qualification in NATA. That means only NATA score is not enough for admission in B.Arch, you must appear or have had appeared in WBJEE and secured a good rank. FYI last year i.e. for 2015, opening and closing ranks for general category were 861 and 4767 respectively.
Hope it helps.

Yes, you are eligible for BA in Political Science.

Yes, you can give the NDA exam during your class 12th, but you have to present your passing certificate or marksheet of class 12th during the SSB interview. So, giving NDA exam during class 12th will surely be helpful to you, as you would get a good idea about the pattern and level of written test. But, it will not be valuable for your selection, as you will not be eligible for SSB interview. In a nutshell, though you would not be selected, but I recommend you to surely give the NDA test at least once during your class 12th.

https://www.shiksha.com/b-tech/colleges/b-tech-in-food-technology-colleges-india
You can shortlist your desired colleges from the link above.

U can get a seating SPAV (school of planning and architecture Vijayawada). .

Please check for your eligibility to pursue B.Com from Ramanujan College at the link provided below:
https://www.shiksha.com/accounting-commerce/course/b-com-ramanujan-college-kalkaji-delhi-259032